The cap can be removed but it is difficult even for a boat professional and the hull can get warped, distorted quickly.
Need more info on the boat year and model and repairs and what is connecting the cap underneath the rub rail.
Rivets or fiberglass cloth.
Never heard of one that had the cap glassed on. Thats funny.
I know a Nitro 911 cdc is glassed down. They glassed the consoles down and a couple other spots so it basically glassed down the cap. I've seen other boats that have straps of glass connecting the top to bottom. That's funny