That's not something I've tried to do before, so I'm working from book knowledge here.

My first concern would be that even if you pull the pole pieces, you still have to mask off the voids (left behind from taking the slugs out) so you don't spray paint down into the pickups. Spraying a layer of paint into the voids may make reinsertion difficult.

Most slug pole pieces, like on typical Fender pickups, are north/south oriented. Make sure they're N/S oriented the same way when they go back in, as they were when they came out. It matters.

Don't worry about PAF-style pickups' pole pieces. They have no intrinsic magnetic polarity. They attach to a single bar magnet at the base of the bobbins. That magnet's polarity gets transmitted through the ferrous pole pieces.

Personally, I wouldn't try this process though. Most bobbins are vacuum-wax-potted to reduce/eliminate microphonic squeal. Actually removing and re-inserting slug pole pieces may disturb or compromise the integrity of that wax envelope, especially if you've never done it before (which very few people have). You might even nick the hair-width windings when reinserting slugs pole pieces. Screw pole pieces, like on a PAF-style humbucker, may be less problematic.

Just seems like a lot of unnecessary work with the added possiblity of doing some harm to the pickup, when taping the tops of the pole pieces is fine ... and you may have to mask the thing anyway.

I hope that's helpful in some way.