As a final consideration of how bad it could get, consider what is on
the other side of the wall the shower faucet is on. If it's a closet,
or a room where you can easily just repaint a wall, then if you get
screwed up and have to replace the whole thing, it still isn't too bad,
as you have easy access from the backside.
If, on the other hand, it's an outside wall or similar, then I think
you're going to have a much bigger problem if total replacement is