I've done a lot of metal prep and painting (autobody). The backs on the XA/XA2 are simply too smooth to have finished with paint as they did. The back is the only metal surface on the camera and looking at the paint too hard will cause it to pop off in chunks on some of the cams
The trouble it would take to properly prepare and finish the back is a bit more than I ever wanted to pursue.
Find an XA2 with a really nice back. They are cheap because of the automation. (Personally I have switched to the XA2 as a better camera because of the XA squinty rangefinder and unreliable dual needles to show shutter speed). I use XA2's now.
Take the bottom off the camera.
Use a good needle nose plier.
Get a grip on the hinge pin at the slot where the strap goes.
Slide the pin out the bottom.
Do this with both cameras.
Exchange backs and slide the hinge pin in from the bottom.
Replace the bottom of the cameras.
15 minutes... with fumbling.
Never let the camera lie on it's back. Make a velvet pouch for it. Threaten mayhem to any other person who touches the camera. The black paint may stay on, as long as you don't sneeze near the camera when it's out of the velvet pouch. Consider hiring guards for when you cannot monitor activity around the camera.
Actually the back switch trick is your best option. The last XA2's I bought, I paid $20 for two. Both of them work better than my 2 XA's. They do vignette a touch more, but I like the effect.