I've always done these by spraying the whole thing with a coat of epoxy primer first, then spray the push button. After that, mask the button off with masking tape. The tape can be slipped under the edge as you press the button down.
No big deal...

The push retainer idea sounds interesting...
If one were intent on disassembling it, I think putting on the reading glasses and using a couple tiny screws to replace the original peened fastening would work well.