Recently updated my 25+ yr.-old bungalow bathroom. New vanity, fixtures, etc. All I want to do is upgrade to a new Delta tub & shower trim. I have no plan to trash my wall, and from everything I've read, I shouldn't have to. I have the Delta "classic" the inexpensive, basic model with acrylic turn knob. I finally found the Delta Becker Monitor (14, I guess) trim that I want. A plumber told me the new model number won't work with my current model. He's pretty-much insisting that he go into the wall to redo the setting, or whatever you call it. (I do have an access panel, but it's behind very heavy furniture which I do not want moved, nor should I have to.) Can't the trim kits simply be switched out?