I would assume that if Tremere had diablerized the Tzimisce antediluvian, he could transubstantiate the Tzimisce Clan weakness, but its only a theory... I also have the Tzimisce Civil War taking place until 1451, with the Old Clan Tzimisce allying themselves with the Tremere, which would theoretically give the Tremere Koldunic Sorcery as well....