His capacity is reduced immediately when he get controlled, before it can be merged with the base version.
201345
Tariq, The Silent
G2Sabbat: While Tariq is controlled, he gets -4 capacity. He can strike, ranged: steal 1 blood or life (becoming blood). Black Hand. Red List.
Independent: Tariq's capacity is not reduced by his card text.
Rulings
When he merges (in whatever way), he becomes independent and any Anarch token is burned.
Black Hand is not a title, it is a trait unrelated to any sect. The trait is not lost if the vampire changes sect.