You're just in luck. Over at Mod the Sims, there is a Sorcerer Mod that makes your Sim a Sorcerer by a CAS trait, you should definitely check it out. So far it works really nice and is compatible with the latest patch.
http://modthesims.info/download.php?t=594052
I personally disagree with your idea just because I want more lifestates in the game, especially Witches! The supernatural aspect of the Sims is always a personal favorite. So if an when Witches get added, you could not buy that and instead use the Mod that I stated above!