Question for the plumbing inclined

So I bought a apartment-turned-condo a while back, and once I moved in I noticed something wrong with the faucet in the bathtub. It’s one of those pull out to turn on, twist to adjust temperature ones. I noticed sometimes when I’d push it to turn off the flow, I’d still get a trickle of water coming out. Upon closer inspection, I noticed the metal surround thing around the knob was quite a bit bent … at that point I had a limited home warranty, and called in a plumber. He took things apart, hmm’ing and ah’ing the entire time. Turns out, the contractors who refurnished the tub had used a valve (I guess that’s what it’s called, the metal part that connects to the pipe in the wall that controls the water flow) that was too short for the depth of the wall/tub. So to counteract this, they banged on the surround to try and get the knob to recess as far as possible to make it not leak. At one point I bought a new knob and surround to try and fix things, but noticed that if I installed it by the instructions and screwed the knob in all the way, the water was on like half-way all the time. Instead of being flush with the surround just outside the wall, it’s like it needed to be flush with like half an inch into the wall.

My question is about how to proceed. Do they make longer/deeper valves that I can buy and just swap out? The plumber (not the greatest, IMO) kind of insinuated that I’d need to put in a spacer or something. My biggest concern is that, while I’d like to do it myself, my unit and the one below me share the same shut-off valve, so any repairs must be done in a timely fashion, not my inept-ghetto rigging I usually use. Any suggestions would be appreciated, even if it’s a simple ‘You fail, call a real plumber.’
To replace it completely you will need a shutoff valve to the portion of pipe you will be working on. I believe they do make longer single valves but it’s been years since I have had to do one of those. Check your local harware store, they usually have a section just for sink and bath fixture parts. When you install it you have to get it positioned just right or you will get the problem you mentioned before with poor water flow. They can be a pain.

Thanks, I’ll hit up the hardware store before I do anything else.