Yes, you do have to remove the allen head screw. It's holding your disc on. The large bolt is just inside the hole in the disc. No need to touch it. It holds bearings and stub axles inside the rear upright. I removed my rear discs to check the parking brake linings with a couple of whacks from a plastic hammer. The rubber one seemed to bounce off with no shock.
The parking brake shoes are kind of cute, like an itty bitty drum brake without the hydraulics.
If you adjust them, I'd recommend loosening the cable adjustment first. That way, the brakes can be adjusted without the cables interfering. Then, when the shoes work the way you want them to, adjust the cable for the "4 clicks to hold" that the book wants.