If you ever did need to make a hole I listed a bunch of good info on making protectors in this thread starting with post #9 -
https://pinside.com/pinball/forum/topic/clearcoating-over-touchup#post-5706052
I also posted sections about the protector in both of these two restores with pics:
https://pinside.com/pinball/forum/topic/1977-williams-big-deal-barn-find-#post-6157358
https://pinside.com/pinball/forum/topic/1973-williams-gulfstream-restoration/page/2#post-5689156