A baal teshuva’s newly deceased grandfather left in his will that he wants to be cremated. As the only religious family member kaddish will fall to him. Is there any ikuv against him saying kaddish for a cremated grandfather?
Although there will generally not be an obligation to say kaddish for somebody who left instructions to be cremated, it appears from several poskim that it remains permitted to do so.
If he wishes to say kaddish, he therefore can.
See: Rema (Yoreh De’ah 376 (no obligation of kaddish); for those who nonetheless permit saying kaddish, see Shut Radach (Beis 30; this is actually the source of the Rema); Kesav Sofer (Yoreh De’ah 171); Chesed Le-Avraham (Tinyanah 81); and see Iggros Moshe Yoreh De’ah 4:61), who writes explicitly that the Rema only means that there is no obligation to say kaddish.