I want to replace the bathtub spout with a new one available at hardware store.
I tried unscrewing the old spout barehanded and it won't budge. Can I use a wrench (I don't care if the old spout is marred), or is there a danger of breaking the pipe in the wall. I do NOT have access to the valves, etc. in the wall. I just want to change the external fixtures.

Hey Bob,

If the spout's old then it's a chrome over brass screw on metal spout.
These spouts are connected to a galvanized ell by a galvanized nipple.
Putting a wrench on it and turning it out counterclockwise is about the only way you're going to remove it. Be advised that the nipple might also come out. Don't panic!
Simply wrap the threads with Teflon Tape and reinstall with the new spout. Be certain that the threads in the new spout match the depth of the old one Some spouts have threads that are deeper up in the spout then others.
Good luck. Tom