The Torah portion of Ki Savo:
In the sixth Aliyah the Torah portion discussing the curses is read.
Avoiding an interval by the curses: The custom is not to make an interval of Aliyos by the curses of Ki Savo. One is to read from at least three verses prior to the curses and conclude at least three verses after the curses. [The need to add three verses after the curses refers to Parshas Bechukosaiy in which there remains three verses prior to the end of the Parsha. However, in Parshas Ki Savo one reads only one verse after the curses, being that it represents the conclusion of that Parsha.]
Not to call up by name: The custom is to not call anyone by name for the Aliyah of the curses, which is the 6th Aliyah, and rather whoever desires goes up for the Aliyah ]without being called[. [Many are accustomed to designate this Aliyah to a specific person and in such a case] one is to avoid going up for this Aliyah in place of the person that it is set to be given to. [Many are accustomed that the Baal Korei himself is designated to receive this Aliyah. Practically, this is the Chabad custom. The Baal Korei is not called up by name and hence begins the blessings on his own. The Baal Korei may receive a Mi Shebeirach with his name after the Aliyah.]
Reading the curses in a low voice: The custom is for the reader to lower his voice upon reading the curses. He raises his voice again only by the words “Eilu Divrei Habris” in the end of Shishi.
What is one to do if the Baal Korei is a Kohen [or Levi]?
As brought above, many are accustomed [and so is the Chabad custom] that the Baal Korei receives the Aliyah of the curses. If the Baal Korei is a Kohen [or Levi], then some Poskim rule he should read seven Aliyos prior to the curses and then go up and read the curses as an eighth Aliyah. However, it is not allowed for the Kohen or Levi to go up for the curses if it is still the 6th or seventh Aliyah. [Practically, however, according to the Chabad custom the Baal Korei may not add or change the Aliyos. Therefore, the Kohen is not to go up and rather another person should do so without his name being called.]
What is the law if the Gabaiy absentmindedly called someone up for the Aliyah of the curses?
The person who was called up should go up for the Aliyah.
Custom of some communities to not read the Parshiyos of Bechukosaiy and Ki Savo: See Biur Halacha 428:6 “Bepesukim” who severely negates this practice.
 One does not make an interval in the reading of the curses in Bechukosaiy, and reads from three verses prior and three verses after the curses. However, by the curses of Ki Savo one may make an interval, [as they were said by Moshe in the singular tense and hence are not as severe-M”B 428:18]. Nevertheless, the custom is not to make an interval even by the curses of Ki Savo. [Michaber ibid]
 Michaber ibid
 M”A 428:8
 M”B 428:16
 Rama 428:6
 The reason: As we suspect that if one is called by name he may not want to go up for the Aliyah and will despise the curses [as well as doing so shortens one’s life-Brachos 55a]. Hence, one is to arrange in advance who is to receive this Aliyah. [Levush 428; M”B 428:19; Biur Halacha “Beshmo”; Kaf Hachaim 428:40]
 M”A 428:8 in name of Mahril “The Mahril despised those that went up for the Aliyah as it is only to be given to the Shamash who is hired for this purpose.”
Will something evil befall one who receives this Aliyah? Those who go up for this Aliyah suspect that something evil will befall them. However, certainly if one is doing so out of respect for the Torah, nothing evil will befall him. [M”B 428:17] The Sefer Chassidim 766 states that in previous generations they would call an ignoramus for this Aliyah in order so the evil does not befall a Torah scholar. Nevertheless, if a Torah scholar was called up he is not to refrain from reading it. [brought in Kaf Hachaim 428:34] The Kneses Hagedola states that no evil will befall anyone, as one has no intent to recite curses at all. [brought in Kaf Hachaim ibid] In Shaar Hakavanos p. 73 and Peri Eitz Chaim it states that the Arizal went up to the Torah for this Aliyah and read the Torah as is the Sephardic custom.
 M”B 428:17 “This is a proper custom”; Kaf Hachaim 282:8; 428:35 “So is the custom today”; Darkei Chaim Veshalom 203
 Hayom Yom p. 88; Sefer Haminhagim p. 31; See Otzer Minhagei Chabad p. 19
 Hiskashrus 840
 Peri Chadash 428:7; M”A 428:8 in name of Kneses Hagedola regarding Parshas Haeigel; Kaf Hachaim 428:38; Hiskashrus 840. In Shaar Hakavanos and Peri Eitz Chaim it states that the Arizal went up to the Torah for this Aliyah and read it in a loud voice.
 M”B 428:17; See Biur Halacha 428:6 “Bepesukim”
 See Rama 135:10
 Tzemach Tzedek 35 [Custom of Alter Rebbe who was the Baal Korei]; Sefer Haminhagim p. 31; Igros Kodesh 3:31
 So is evident from the Poskim ibid that it is forbidden to refuse the Aliyah, as it is for this reason that we don’t call anyone up for the Aliyah in order so they do not become challenged with the desire to refuse it, which is forbidden.