This is where the no-demolition question matters most, because downtown bathrooms often contain tile that simply cannot be replaced.
You may not need to open the tile
Many valve repairs are reached through the existing trim plate or an access panel, and where real access is needed it is usually a small opening in an adjoining closet or hallway wall rather than the shower face. Before agreeing to remove original tile, ask whether the valve can be reached from behind. The answer is often yes.
Period tile is irreplaceable
Hex floor tile, subway tile and original glazes cannot be matched. Working around them takes longer and is nearly always worth it.
Stiff or scalding valves
Old mixing valves degrade slowly until someone is scalded when a tap runs elsewhere. Replacing the cartridge restores control, and on older valves a rebuild kit sometimes preserves original trim.
Stains on the ceiling below
The pan, the drain connection, or grout letting water past the pan edge — three different repairs. In a historic house, finding out which before opening anything is the difference between a targeted fix and losing a bathroom.