You mean to say that the access from the rear is even more difficult than tearing out the tile.
Yes.
The other side of the tub/shower is in the attic area of the main level of the house right where the hip joint of the roofline is - we live in a split level & the section of wall in the kitchen where the top row of cabinets is located.

Far better to remove some of the tile & backer, replace the valve & shower head - then repair that area.