Is there a way to cut and re-thread a shower pipe that is already coming out of the wall?

You Can but typically the pipe for the shower head that is coming out of the wall is just a short piece of pipe that you should be able to remove easily enough by unscrewing it. Then you can just replace that piece with a new one. == Answer== Do the same as above but make sure your shower arm is not floppy, if it is you could tear up the riser coming to the arm. Be very carefull.