Is it possible to convert a press fit bottom bracket to threaded?
BB30 and PF30 have press-in adapters available that have ISO aka BSA aka English threads. They do work but they mostly exist for the purpose of being able to run a certain crank that you wouldn't otherwise be able to, and to a lesser extent to address creak. (I don't have a very refined opinion on how good they are at doing the latter).

BB86/92 and conceptually similar pressed standards (BB90, 95, others) are by nature too wide for this sort of approach to work.

You can make a very effective bearing press for all types of press-in bottom brackets out of threaded rod and some nuts and washers. If you got the right diameter rod to interface snugly with the bushings in the Park BBT-30.4 or 90.3 (for example), you could just get those and skip buying a shop-type press, and you'd have lost nothing but a little bit of speed. (Improvising tools to do the whole job for cheap is kind of a larger discussion and I'm tempted to write more, but it's probably off-topic for this question.)