Guest
1. If copper is attached to the galvanized piping it is the galvanized piping that will corrode.
2. Change the riser pipe to the shower head now while the wall is open.
3. Definitely have the plumber install a brass nipple in between the copper and galvanized piping. This will help prevent deterioation of the galvanized piping. I have had a similar situation in use for 5 years without any problems.
4. I would definitely change the pipes in the wall while it is open.
