I glued everything first on the tank, then paint them. The only thing I didn't glue to the tank prior to painting are the tools, spare tracks, etc.

And if I need to glue things on the tank after painting, I simply glue them directly on to the paint. Even a small dab of glue is enough to hold everything in place. It's not as super-strong bond as a plastic-to-plastic bonding, but from my experience, gluing directly to the paint is more than enough to hold things in place.

In fact, there were times when I'm about to repaint a tank, that I sometimes have trouble removing some tools, even though I simply glued them directly on top of the paint.