Psalm 49: In the house of a mourner, the congregation recites Psalm 49 after Shacharis and Mincha.[2] It is not recited after Maariv.[3] [It is recited after Mishnayos and Kaddish Derabanan.[4]]  The Avel is also to recite Psalm 49 after Davening and conclude the last verse out loud.[5] Kaddish Yasom is recited after the conclusion of the Psalm.[6] On days that Tachanun is omitted [i.e. Mincha Erev Shabbos, Rosh Chodesh, Chanukah, Purim, Nissan, Tishreiy, starting from after Yom Kippur, etc] Psalm 49 is not recited.[7] Many are accustomed to recite Psalm 16 in its place, which is then followed by Kaddish Yasom.[8] On Shabbos, Yom Tov, Chol Hamoed, and Purim, no Psalm is recited.[9]

[2] Beir Hagoleh 393 as custom of Sephardim; Mavor Yavok Sifsei Tzedek 7; Kitzur SHU”A 207:5; Sefer Haminhagim p. 36; So was the custom during the Shiva of the Previous Rebbe; See Nitei Gavriel 99:1; Pnei Baruch 10:29

Other customs: Some are particular not to say this Mizmor during Shiva. [Darkei Chaim Veshalom 1030]

[3] Implication of Sefer Haminhagim ibid which omits Maariv; Custom of Rebbe recorded in Yoman of 5748 that it was not said after Maariv in the Shiva home

Other customs: Some are accustomed to reciting Psalm 49 before or after Maariv. [Beir Hagoleh ibid; See Gesher Hachaim p. 162; Pnei Baruch ibid]

[4] See Q&A!

[5] The custom of Rebbe Rayatz, written by the Rebbe in Reshimos p. 413 [printed in Shulchan Menachem 5:273] was to say it quietly, and have another person conclude it aloud; However, the custom of the Rebbe, as recorded in the Yoman of 1988, was to conclude the verse and then say Kaddish.

[6] Custom of Rebbe in 1988, see Hiskashrus 789; Nitei Gavriel 99:2

[7] Daas Kedoshim 376; Custom of Rebbe in 1988, see Hiskashrus 789 [However, see Reshimos p. 413 that Kapital 49 was said also by Mincha of Erev Shabbos, when the Rebbe Rayatz was in Shiva]; Gesher Hachaim p. 162; Nitei Gavriel 99:2; Pnei Baruch 10:29;

[8] Gesher Hachaim p. 162; Nitei Gavriel 99:2; Pnei Baruch 10:29

[9] Gesher Hachaim p. 162; Nitei Gavriel ibid; Pnei Baruch 10:29

[10] Custom of Rebbe in 1988, see Hiskashrus 789; See Shulchan Menachem 5:270 that the Rebbe in 1952, during the Shiva for his brother, said Psalm 49 directly after the Daily Tehillim and said one Kaddish Yasom for both; See Siddur Rav Raskin p. 189 who records a directive of the Rebbe and Rav Dworkin to say it after Mishnayos; See Nitei Gavriel 99:1 that some recite it after Shir Shel Yom in order to diminish in Kaddeishim; See Reshimos 5 [printed in Toras Menachem Tziyon p. 28] that when the Rebbe Rayatz sat Shiva for his mother the Mishnayos was said after Kapital 49

[11] Custom of Rebbe in 1988 [However, see Reshimos p. 413 that Kapital 49 was said also by Mincha of Erev Shabbos, when the Rebbe Rayatz was in Shiva]

[12] Nitei Gavriel 99:1