If you want to go more lenient and flavorful this way, I think I will add in more graviturgy for my astrologer to start. Would certain aspects of cosmic magic like time travel still be forbidden? Perhaps the rulings on these are more about particular uses and spells rather than entire forms of magic.

Sure, drawing the life-force out of your classmates is I'll advised, but what about calling a spirit to ask it questions about the past? I'd rule both as necromancy but one is clearly harmless.