I have recently replaced an old leaking shower manifold (three handle) with a one handle model. In hindsight I should have used an adapter plate like this one to cover the two outer holes and expose one larger hole in the middle. Instead, thinking I would cover two holes I might as well cover three, so I moved the new knob up to a more comfortable height and cut a new hole, installing the new manifold and knob there. This is now all working.
I still have the three holes from the old knobs. I'm wondering the best way to cover them. I was thinking about finding a few pieces of decorative tile (each slightly larger than a hole) and affixing them over each hole. If I do this, how would I affix the tile? I'm assuming I would caulk around them after doing so, but would caulk be enough for hold (This thread gives me pause)? Can you think of other ways to cover the holes? Note of course that the tile is old and certainly cannot be found.