If you have to remove 4 tiles to get to the valve, then you're removing far more of the surface waterproofing than I'm comfortable with. Especially if this was done with a modern vapor barrier in place or membrane. I'd MUCH prefer to go through the rear and affect the watertight integrity of the shower as little as possible. I don't know what brand of valve you picked, but pick the best quality that you can for this second go around.

Thanks for the comments. It seems to make sense to go in from the back through the closet. Only one other problem that I forgot to include in the first post. The size of the trim plate for the new valve is smaller than the opening that was cut in the tile for the original valve. (No one makes a plate as wide as the current opening - 9 inches) So some how going to either have to fill in the gaps or replace that one tile.

Köhler has a basic volume control valve and a separate thermostatic valve to control water temperature. Other companies, such as Moen offer a combined temperature/volume control valve. Kohler does not. The incoming water is first routed to the thermostatic valve, then to the volume control valve. The thermostatic valve contains a safety device, required in most jurisdictions, keeps the water temperature balanced. If Junior flushes the toilet downstairs, you don't suddenly get a surge of hot water through the shower -- which is always uncomfortable, and could be dangerous. Kohler 2975 Thermostic Valve There is, however, no such thing as an actual Purist valve. All Kohler styles use the same valves. The valves are fitted with wall trim to hide the valve and give you the Purist look. The same valve could be fitted with Honesty® or Georgeson® or Antique® trim for a different look . You buy the valves, then the trims separately. The valves you need are probably Kohler parts 2975 and 2977, but check with your plumber to be sure. Kohler Purist Valve Wall Trim with Cross Handles If you have more than one shower outlet -- for example a shower head and body sprays (or tiles, as you are calling them), you use a separate volume control valve for each outlet. If you have a tub/shower combination, a separate volume control valve is used to divert water to the tub spout. You can use up to four volume control valves -- one each for the shower head, body sprays, tub spout and and hand shower, for example. Four isusually the practical limit because you probably don't have the water pressure for more than four. All can be turned on/off and volume adjusted separately -- but all would be at the same temperature which is controlled by the single thermostatic valve. If you want separate temperature controls, you would need a separate thermostatic valve for each device -- which is usually overkill -- and expensive. You don't necessarily need a volume control valve at all, especially if you are using just one shower outlet. If you elect to not use one, then the water is directed to the shower head at full water pressure -- The shower head has a built-in limiter that keeps volume restricted to 2.5 gallons per minute. This limit is required by the Energy Policy and Conservation Act in the U.S.

This is another bathroom that didnt have any gaps with the tile and no gaps on the actual valve trim kit as a comparison.