Dumb Lilith question - if I equip a spellset that gives me treasure hunter, can I swap to my normal DD spellset after hitting her once at the start of the fight? Will the TH effect remain?
Yes, just as with normal TH as soon as it’s applied, it’s on and you can then fight as you normally would.
As Lowen said, you’d be better off with TH items or even just subbing THF outright or a combination of the two if available (Chaac Belt is TH+1 and easy to get). You don’t have to mess with the spells if you don’t want to.
Or perhaps you were asking if the TH value from spell vanishes if you change spell sets mid fight? To that one, I have no Earthly idea. If applied from gear, everything stays put but if applied from trait and trait just... goes poof? No clue. I *THINK* it would stay put?