I take off the parking brake lever, and (IIRC) put the nut back on.
Then I place a large socket over the nut and shaft, and use a C-clamp to press the piston back in. Always feels a little bit "dicey", but then it always works.
If you can find "Ogre's cave", through the link on Pennocks, he goes into a long dissertation about how to do it.
My take? Pretty much if you do it, and don't break anything, and your parking brake still adjusts and works, you're golden.
With that said... since '97 when I "got back into" Fieros, I've had one pre-88. Never could get the brakes right on that one, for whatever reason.