The Seder and the Haggadah
It has been a tradition in the household of the respective Rebbeim, handed down from generation to generation, to begin the First Seder immediately after Maariv and not to dwell on it at length, so that the Afikoman will be eaten before midnight. The Second Seder, by contrast, begins later in the evening, and the Rebbe speaks at length expounding the Haggadah, sharing Torah insights, and arousing his listeners in their Divine service. 
(b) The Seder Plate (Ke'arah):
In the Rebbe's household the [three] matzos are placed not on a plate but on a cloth, except for the matzos of the Rebbe, which are placed on a silver tray. 
It is customary to choose concave matzos, suggesting the shape of a vessel which can serve as a fit receptacle [for the downward flow of Divine light].
The matzos are separated from each other by napkins.
The Bone (Zeroa):
We use part of the neckbone of a fowl, and make a point of NOT eating any of its meat in order to avoid any similarity to the Paschal sacrifice [which cannot be offered in the absence of the Beis HaMikdash].
For this reason the Previous Rebbe would remove almost all the meat from the bones of the zeroa.
The Egg (Beitzah):
The egg is cooked until hard. It is eaten, in commemoration of the Chagigah, even when erev Pesach falls on Shabbos, despite the fact that in Temple times this festival sacrifice was not offered when these days coincided.
For some years now processed ginger and cinnamon have not been included, for fear of some admixture of chametz during their processing. The ingredients used are apples, pears, nuts [and red wine].
Our custom is to use [raw] onion (or [boiled] potato).
The Bitter Herbs (Maror and Chazeres):
We use both chazeres (romaine lettuce) and horseradish for both maror and korech.
(c) Kiddush and Havdalah:
It is our custom to stand while reciting [the evening] Kiddush on Pesach and likewise on the eve of Shabbos and of all festivals.
For customs involving the Kiddush cup as practiced in the Rebbe's household, (see p. 55 in the printed version and in the electronic version see the section called Kidush).
Even when a festival falls on a weekday, the text of Kiddush reads U-mo'adei (with the prefixed vav), just as on Shabbos the preceding word reads V'Shabbos.
On Pesach one drinks the entire contents of the cup of wine (Bach, sec. 472) without pause (Magen Avraham, loc. cit.). This is the custom in the Rebbe's household, and it applies equally to the remaining three cups.
The custom in the Rebbe's household when a festival falls at the conclusion of Shabbos is not to place the lights next to each other for Havdalah, nor to join them at their wicks, nor to look at one's fingernails. When reciting the blessing Bo-re Me'oreh Ha'esh one merely looks at each of the candles.
(d) Text and Procedure:
It is not our custom to wear a kittel (white robe) for the Seder, nor to be particular about which direction one faces.
Eating the Karpas:
The karpas is eaten without reclining. The Rebbe Shlita notes that at the table of the Previous Rebbe he did not observe that the remaining pieces of karpas were replaced on the Seder plate; thus from this point on only five items remain.
The [middle] matzah is broken while still covered in its napkin.
The Rebbe Rashab (and it goes without saying that his son, the Previous Rebbe, did likewise) used to break the Afikoman into five pieces. When it once happened to break into six pieces, he placed one aside.
Some have a custom whereby children snatch the Afikoman [and then ransom it in exchange for a gift], but this is not done in the Rebbe's household.
Our custom is to preface this passage with the following in Yiddish: "Father, I'm going to ask you four questions."
This is said even if the father is no longer living. The passage is then read and translated in paraphrase, as follows:
"Why is this night of Pesach different than any other night of the year? The first question is: On all other nights of the year we do not dip...we do so twice: the first time we dip karpas in saltwater, and the second time we dip maror in charoses!' The second question is:...."
After the youngest present had finished reciting the Mah Nishtanah as above, the Previous Rebbe would repeat it in an undertone, complete with its introduction and Yiddish translation.
"The cup is now raised" [before Vehi SheAmdah]:
The custom of the Rebbe's household is that the matzah is covered first, and only then is the cup raised, in keeping with the instruction at the end of this paragraph, that "the cup is replaced and the matzah uncovered."
This procedure applies also to the paragraph that begins with Lefichach.
The Ten Plagues and Acronyms:
One spills a little wine from the cup as each of these acronyms is read, and only thereafter is wine added to the cup.
Matzah Zo; Maror Zeh:
One holds the broken matzah in his hand and says: "Matza Zo".
[One takes the maror in his hand and says:] "Maror Zeh":
The custom in the Rebbe's household is to hold the middle and lower matzos in their covering until the second Al shoom mah of the former paragraph. When mentioning the bitter herbs, however, it is the custom in the Rebbe's household to rest one's hands on the maror, as well as on the maror to be used for the korech until the second Al shum mah of the latter paragraph.
One covers the matzah [and raises the cup] [before Lefichach]:
Siddur Torah Or, p. 188b, cites a gloss of the Tzemach Tzedek on this phrase: "And one holds it until the conclusion of the blessing, Asher Ge'alanu."
According to the custom of the Rebbe's household, however, the cup is held only until one has concluded saying Venomar Lefanav Halelu'ya.
It is then replaced on the table, and taken up again for the blessing that begins, Baruch.... asher ge'alanu.
Al Achilas Matza:
When reciting the blessing Al Achilas Matza one has in mind that it refers [not only to the kazayis of matzah about to be eaten but] also to [the korech and to] the Afikoman [at the end of the meal].
Nevertheless, though one should avoid any irrelevant talk before eating the korech, it is not the custom in the Rebbe's household to extend this stringency to the eating of the Afikoman.
One then breaks off a kazayis from each [of the two upper matzos]:
Both are used, because some hold that the kazayis (one ounce; 25.6 grams) that one is required to eat should come from the upper matzah, while others hold that it should come from the middle one.
One does not dip [the matzah] in salt:
This is the custom in the Rebbe's household. 
And they are eaten together:
I.e., [the kazeisim from the two upper matzos] are put into the mouth simultaneously. This way there will be no interval between the blessing for eating matzah and the eating of the relevant kazayis which, as explained above, comes from either the upper matzah or the second. (Tur Shulchan Aruch.)
Maror (the bitter herb)...is dipped in charoses
Only then does one recite the blessing, so that the mitzvah [of eating maror] should immediately follow it. It is preferable not to dip the whole kazayis of maror in charoses, so that the bitter taste will not be neutralized.
And one recites the blessing of Al Achilas Maror
When reciting this blessing it is our custom to bear in mind the maror of korech as well. 
Korech (the sandwich of matzah and maror) ...is dipped in charoses
The chazeres alone is dipped, but not the matzah.
Those who are most particular about keeping their matzah dry do not dip, but put some dry charoses on the chazeres, and then shake it off. This is the custom in the Rebbe's household.
Shulchan Orech (The Festive Meal)
Our custom is to eat the festive meal without reclining. On both nights one starts the meal with the egg (from the Seder plate) dipped in saltwater.
Particular heed is to be taken to avoid wetting the matzah: 
For this reason the matzos on the table are kept covered, so that no drop of water should fall on them, and so that no matzah crumbs should fall into any water or soup. Likewise, before pouring water, or other liquids containing water, into a cup or plate, one should check for any crumbs of matzah.
The Rebbe Rashab would never eat [shemurah] matzah together with fish or meat lest it become wet, though he did eat matzah together with wine.
When washing the hands in the middle of the meal, and so too at mayim acharonim [at the end of the meal], one does NOT pass one's fingers across the lips [as one usually does]. (This applies to the first seven days of Pesach, but not to Acharon shel Pesach, the eighth day, when we make a point of wetting matzah.)
Tzafun (Eating the Afikoman)
Ideally one should eat two kazeisim one to commemorate the Paschal Lamb Offering (the Korban Pesach), and the other to commemorate the matzah that was eaten together with it. (The Alter Rebbe's Shulchan Aruch 477:3.) This is the practice of the Rebbe's household.
If one finds this difficult, and therefore will eat only one kazayis, he should intend that it serve to commemorate which-ever of the above two subjects is ultimately the one requiring commemoration.
One must be mindful not to drink after the Afikoman
The unqualified expression "not to drink" in the Alter Rebbe's Siddur implies that
- even water is to be avoided, and that
- this restriction applies equally to the Second Seder.
This, indeed, is the accepted practice.
It is not the custom in the Rebbe's household to make a point of completing the recitation of Hallel before midnight (in contrast to the eating of Afikoman on the first night).
(The Grace After Meals): For the relevant customs and textual variants, see p. 43ff., above in the printed text and "Grace After meals in the electronic version).
The Cup of Elijah
The cup is filled after Grace (except [in the Rebbe's household] at certain times). The Previous Rebbe, following the tradition of all his forebears, made a point of filling this cup himself.
And the door is opened
The custom in the Rebbe's household is that (when Pesach falls on a weekday, a lighted candelabrum is taken in hand, and) all the doors between the room where the Seder is conducted and the outside are opened.
The passage beginning Shfoch is then said, those sent to open the doors saying it at the front door. The Previous Rebbe, accompanied by one of his household, once went to open the door himself, and on that occasion he recited this passage at the door.
Those who were sent to open the doors are waited for, and the following passage (beginning Lo Lanu) is recited on their return.
There is no need to stand while saying Shfoch Chamascha.
The four verses beginning Hodu L'Hashem
The elder of the household (or the cantor, whenever Hallel is recited in shul throughout the year) says the first verse, and all those present respond by repeating this verse and proceeding to say the second. The leader, having repeated the first verse together with his listeners, then says the second verse; those present again respond by saying the first verse, but this time they proceed with the third verse. The same procedure applies to the remaining two verses.
The four phrases beginning Ana:
Each of these phrases is first said by the leader, and then repeated by all those present.
The second passage beginning with Hodu L'Hashem
(the Great Hallel; i.e., Tehillim 136)
[In the Great Hallel, whose verses total 26, the numerical equivalent of the Four-Letter Name of G-d], one bears in mind the letter yud [which equals ten] while reading the first ten verses, the letter heh [five] while reading the next five verses, and so forth, [as indicated in the Siddur; i.e., the letter vav (six) while reading the next six verses, and the letter heh (five) while reading the final five verses].
It is not the custom in the Rebbe's household to recite the concluding hymns which are to be found in most Siddurim and Haggados.
After saying Leshana Habaah B'Yerushalyim the Rebbe customarily pours the wine from the Cup of Elijah back into the bottle, while all those present sing E-li ata V'odeka to the tune which is one of the ten melodies composed by the Alter Rebbe.
One does not say Chasal Sidur Pesach ("The order of Pesach is now completed"  ).
The Seventh and Eighth Days of Pesach
There is more festive rejoicing on the Seventh Day (Shevi'i shel Pesach) and on the Last Day of Pesach (Acharon shel Pesach) than on the preceding days of the festival. 
It was the custom in Lubavitch to stay awake throughout the night of the Seventh Day of Pesach, as well as on the [first] night of Shavuos and the night of Hoshana Rabbah.
One should study Torah all night. 
The congregation stands during the public reading of the Shirah [i.e., the Song of the Sea; Shmos 15:1-19]. 
At the evening and midday meals of the Last Day of Pesach it is customary to wet the matzah. 
On the Last Day of Pesach, when the fingertips have been washed with mayim acharonim at the end of the meal, one resumes the usual practice of passing them over one's lips.
After Mussaf on the Last Day of Pesach the preferred procedure is to recite Kiddush, and then to pray the Minchah service before the [midday] festive meal. 
The Baal Shem Tov would partake of three meals on the Last Day of Pesach. He used to call the third meal of that day, Mashiach's Seudah ("the festive meal of Mashiach").
The Period of Sefiras HaOmer and Lag BaOmer
It is our custom to refrain from reciting the blessing She-he'che'yanu during the period of the Counting of the Omer. 
During these [forty-nine] days, in addition to one's regular studies, one studies a page per day of Tractate Sotah. 
With the Mitteler Rebbe, Lag BaOmer was one of the outstanding festivals. He would go out into the fields with his chassidim and partake of a light meal which included spirits and hard-boiled eggs, and which was accompanied by singing and dancing.
On those occasions supernatural happenings were often to be seen. 
According to time-honored custom, chassidim used to get together on Lag BaOmer and sit down to farbreng between Minchah and Maariv. 
- (Back to text) Introduction to Likkutei Dibburim, ch. 23 [and in English translation: Vol. III, p. 89]; cf. HaYom Yom, p. 45.
- (Back to text) Perhaps this applies only at the Rebbe's table, whereas elsewhere one should use a plate, since the AriZal writes that a plate represents the all-encompassing attribute of Malchus. See also Bamidbar Rabbah 1 3:14 ("The plate corresponds to the sea") and Meorei Or, s.v. Kaara (Note by the Rebbe Shlita.)
- (Back to text) [The first would thus literally mean, "in the year that has come," while the second would literally mean, "in the year that is coming"; cf. Rashi on Bereishis 29:6.]
- (Back to text) This requires explanation, for the Shelah writes that according to the writings of the AriZal one should dip the matzah in salt. See also sec. 8 of the Biur that explains the maamar beginning Lo Tashbis Melach, in Likkutei Torah. (Note of the Rebbe Shlita)
- (Back to text) The Rebbe Shlita notes: "It is surprising that the Alter Rebbe does not mention this in his Siddur [where his edition of the Haggadah appears], even though he does write it in his Shulchan Aruch (475 :18)."
- (Back to text) [Matzah which has become wet is known as matzah sheruyah (lit., "soaked matzah").]
- (Back to text) [The reason: Chassidus teaches that the prime spiritual task of Pesach - liberating one's soul from the stultifying constraints of one's own House of Bondage - does not end with Pesach. This task is ongoing, year-round, lifelong.] 314. See Sefer HaSichos, Summer 5700, p. 71; Likkutei Sichos, Vol. II, p. 545; op. cit., Vol. IV, p. 1298.
- (Back to text) HaYom Yom, p. 47.
- (Back to text) Such was the custom of the Previous Rebbe. [Cf. the passage on Shulchan Orech on p. 79, above.] The purpose of this custom is to differentiate between the first seven days of the festival and the Last Day, in the same way as we do not recite the blessing Leshev Basukah on Shemini Atzeres, even though [outside Eretz Yisrael] it is our custom to eat in the sukkah throughout the day.
- (Back to text) HaYom Yom, p. 47.
- (Back to text) Ibid. It will be noted that the Haftorah of the Last Day of Pesach focuses on the theme of Mashiach (Isaiah 10:32-12:6); cf. Likkutei Sichos, loc. cit.
In the year 5666 (1906) the Rebbe Rashab ate this meal together with the students [of the Tomchei Temimim Yeshivah in Lubavitch], and directed that each student be given four cups of wine, saying, "This is Mashiach's Seudah."
It is obvious that this directive was not intended for that year only, but was meant to be perpetuated. (HaYom Yom, p. 47; and see at length in Likkutei Sichos, Vol. IV, p. 1299.)
- (Back to text) HaYom Yom, p. 48.
- (Back to text) Ibid., p. 51.
- (Back to text) Likkutei Dibburim, Vol. III, p. 519ff. [and in English: Vol. IV, Diary entry for 20 Iyar 5656, appended to ch. 30]; HaYom Yom, p. 55.
- (Back to text) Sichah of Lag BaOmer, 5701, sec. 8, p. 119 (reprinted in Kuntreis No. 78: Kuntreis Lag BaOmer, 5710.)
The sichah continues as follows: "Chassidic oral tradition has preserved for us three observations of R. Hillel of Paritch on the above custom. Firstly, there is a difference between Minchah and Maariv. Though this is not much discussed in the Shulchan Aruch, he stated it as if it were an unquestioned halachah that one may sit down to farbreng before Maariv.
Secondly, the law applying to a group differs from that which applies to an individual. And thirdly, as he pointed out, what is davenen all about? It aims to create a sweet state of Divine gratification. And this is precisely what a farbrengen accomplishes..."
On the above-mentioned difference between Minchah and Maariv, the Rebbe Shlita has appended the following comment:
"At first glance, considering the discussion in Tractate Shabbos (beginning of p. 10a), the contrary would appear to be true - that in this matter, the law governing [the time preceding] Maariv is more stringent that the law governing [the time preceding] Minchah. It would seem, therefore, that the point of the above statement is that since Maariv has a longer available timespan, there is more room for a lenient ruling concerning possible interruptions in the time before Maariv; i.e., to permit an interruption to begin a short time before the time for Maariv, according to the view of the Taz (Orach Chayim 235:3). However, it seems that the Alter Rebbe holds that the prohibition to embark on another activity begins half an hour before the onset of the obligation to pray Maariv (Shulchan Aruch, Orach Chayim 431:5).
"An additional consideration in the direction of leniency could perhaps be argued: In our days, unlike in the days of the Talmud and the Shulchan Aruch, a farbrengen before Maariv is an unusual event, which is nevertheless held at this hour on Lag BaOmer (and likewise on Purim) because by nightfall its time will have passed. For this reason, then, it would be inappropriate to prohibit it, as pointed out in the Shulchan Aruch, Orach Chayim 89:7.
"Even if it were objected that `an ordinance whose reason lapses does not itself lapse' (cf. Sdei Chemed, Klalim 3:34), the prohibition in our case could well be regarded as an exception, since at the outset the Sages differentiated between undertaking common and uncommon activities before prayer.
"On this entire subject one should consult Shulchan Aruch, Orach Chayim, sec. 232 and 235 and their commentaries, and the Chiddushei Mishnayos of the Tzemach Tzedek on Tractate Shabbos 1:2. At any rate, this is not the place for any longer treatment of the subject."
See also the sichah [of the Previous Rebbe] of Lag BaOmer, 5704, in Likkut 33, sec. 1 [and in English: Likkutei Dibburim, Vol. IV, ch. 33, sec. 1].