How much suck is this leak repair going to involve?

I seem to have a pinhole leak in 1/2" copper somewhere going up from the basement to the shower (not sure if it's the hot of cold pipe). It's a single knob cartridge style setup. Am I going to have to rip open that wall? Can the pipe be disconnected by removing the knob/cover/cartridge, and then maybe fish down some Pex to replace it? Thank you in advance for your advice, and feel free to contact me for electrical help in return. Happy Friday!