I would NOT apply to the slide and frame rail surfaces. The tolerances would definitely be affected and the finish is probably not durable enough to resist abrasion from sliding parts. Avoid any sliding, rotating, or tight fitting surfaces.
On one episode of the "reality gun shows", they applied a finish (chrome??) to a 1911. I told my wife that they made a mistake in plating everything, including the slide rails. Any gunsmith should know better than that. Sure enough, it would not assemble and they had to grind the surface off.