Arcanist opposition schools and quick study

[Decimus Drake]

So a school savant arcanist uses two spell slots to prepare an opposition school spell and then uses Quick Study to replace this with a non-opposition school spell or spells. Can they select two replacement spells or one, leaving a slot open? Would it be possible to do the opposite? Using a point to replace two prepared spells with a single opposition school spell.

[Rub-Eta]

An Arcanist do not replace filled spell slots with Quick Study, they only replace a spell of equal level (not even lower is allowed). This means that even if you expend two (or any number of) spell slots to prepare a spell you can only replace that spell with one other spell, using Quick Study.

Quick Study doesn't allow you to prepare opposition school spells in one spell slot. As a DM, I would allow Quick Study to be used to prepare opposition school spells by throwing one out (as usual) and also spending one that's open (not throw away two already prepared, as you're only allowed to replace one spell). However, by RAW, it would probably not be doable at all.