I acquired a few of the Athearn "blue box" loco kits years ago. For some reason, the thought of painting the handrails never crossed my mind as I assembled them, and now they are rusty. I figured on carefully using a jeweler's screwdriver to remove them, and sandpaper to remove the rust. For paint, would you use a brush, or spray?
I've used both brush and spray, and it doesn't really seem to matter. Either way, you'll want to glue or solder the handrail pieces together first.