How do you swap faces?

Hi, I've recently discovered the little screw that attaches Thomas' face to his smokebox, and I'm wondering how I can be sure to get the face on and off without damaging such a tiny screw. I have no screwdrivers that fit in the space, and I don't want to rip off the smokebox, but my Mom managed to get the screw out the first time. I was having trouble getting it back in without the screwdriver slipping a bit.