Go for it, these are your ideas after all, just remember to test it before actually stopping on something, you could have some of the abilities switched around, add others etc. Theres a certain feeling you can give the player when hes going up against this traitor that this guy will do anything to win, maybe give him spell shield as an ultimate and add dark summoning as a default? I think it would reflect his personality more since traitors often hide behind others rather than attack directly or run into battle weapons drawn, but again this is just my opinion