Adjusting accuracy on an Elabore Grade 2836-2 and a 2804-2

Out of being unhappy with the -17spd my old Hamilton H644250 came back from its latest service, I bought a 0.8mm screwdriver and have been having a go at dealing it in, along with my H694190 Hamilton wind-up watch. The hand winder is easy to work on and I've got it at a 0spd ! The Khaki Night Pilot is a lot more involved and I'm wondering how many times the four case back screws can be used without damaging them. I've got it to +4spd at present and being Old, Bored with nothing else to do I can't seem to leave well enough alone. Plus it's extremely difficult to see the marks around the fine adjustment screw while the screwdriver is in place. So how tough are those screws and what size are they if something happens to one?
Thanks, John U