The only way we presently know to do that is Salazar's basilisk-transmitted lore, which is now probably only available via Quirrell (assuming he is Tom Riddle and Tom Riddle was the Heir of Slytherin who opened the Chamber of Secrets).

Salazar lived after Merlin, so while he definitely knew very powerful magic, it wasn't pre-Interdict game-breaking powerful. If it had been, then he or one of his heirs would have broken the universe by now.

Hypothesis: Quirrell will teach Harry Salazar's ancient lore, which Harry will then use to "tear apart the very stars themselves" and, in some sense, end the world and its magic.

Quirrel is terrified of Harry destroying the stars; he will not teach him any magic which he imagines could be used towards that end. That may even be the reason he has, as he said, changed his mind about teaching Harry any magical secrets.