Throw any Armor All away. It does destroy plastic.
I dont remember specifically on Fiero, but most GMs Ive worked on, the black trim on the lock is metal, with small bent over tabs on the back holding it to the cylinder. They were stainless, or if black, they were just painted black from the factory. Id just use semi-gloss spray paint like BBQ black. If you put anything on them, you wont be able to paint them at all.