I don't think performance gets used very often, so I'd allow it instead of discipline without a feat. In fact, it's probably more 'optimal' to keep discipline since discipline is the default for resisting mental attacks n' stuff. So I'd give it for free.
I'd probably allow scholarship instead of conviction...or, actually, presence makes more sense.
Lore would stay the same, I think, since lots of stories and songs are based on fantastical creatures and events.
But if you want to have him spend a refresh, there's a stunt called...uh...alternate casting style...it lets you swap out your 3 casting skills for 3 different ones.