Take off the rails if doing full stencil, but not for a touch up.
Twisty nails are easy to remove I find by starting at the back with a broad chisel and lever near the nail till you can get some multi grips/ pliers onto head and simply twist out working your way to the front slowly. Greg from RTBB sells these as you don't want to reuse again.
When refixing make sure it is a nice tight hole or simply put a match stick and pva glue to make existing hole good again.
Give it a go dude, might as well regain the rails too if you rip them off.