Go on google or Amazon and search for shower valves, you’ll find pictures of what’s inside the wall behind the chrome plate you got there… seeing images will give you a better idea of what to expect than anything anyone can describe.

After that, go take the knob off your shower valve (probably the center cap pries out, you take out a screw, and it pulls off), then take off that chrome ring (Allen screw on bottom, or it might just get pried off carefully or unscrew the whole thing, they vary). Have a look… that’ll tell you what your specific type of valve is and if you can do this without making a big ass hole in a wall…

Then figure out what’s on the other side of the wall the valve is on… if it’s a closet, maybe a big ass hole in the wall is ok? A big ass hole in the wall of the shower will involve tile. I’m thinking based on your description that you should 100% not fuck with tile. You’ll get into all manner of special tools, special skills, etc. real quick with tile :) a hole in drywall in someone’s closet might be a homeowner kinda deal though tbh.

Those three things are hopefully enough to answer your own questions, because the real “no bullshit” answer is that it depends… pex, copper, iron, delta, thermo, yadda yadda yadda… The shit inside the wall is as varied as the shit on the outside…

I could do this myself, but I wouldn’t… sink, toilet, ice maker, leak in the crawlspace, move the hose bib outside to the complete other side of the house, replace the water heater, add an expandion tank, all that shit is an immediate “fuck no im not paying soneone to do that, ill do it”, but a shower valve is a hard no :)

Have a look by all means, no harm in checking it out, but I wouldn’t be too optimistic in your shoes.