I was wondering, for the fZ6, does the rear wheel have to be removed, or loosened in order to swap out the rear brake pads?
Replacing the rear pads
do NOT require rear wheel removal.
If you look, you'll see a flat head screw to the upper left, adjacent to the bleeder screw. Remove that screw (part #14 below) and they'll be a bolt (I think an allan key, Part #13 below). That is the only bolt holding the pads in(besides the exterior of the caliper).
Now, that caliper is a "floating" caliper meaning as the pad's wear, it centers itself.
You'll notice two bolts (parts #9 and #15) and 2 rubber boots (that I believe the bolt heads are 14mm, parts #6). Pull those and the caliber will come off and upwards.
Some brake cleaner should be sprayed on the piston and assembly.
With new pads, the piston has to be pushed back in (but should be nice and clean). A "C" clamp, C vise, grip, etc will easily push the piston back in. Now they'll be room for the new, thicker pads. Those rubber boots and the bolts that go thru them need to be cleaned and re-greased for SMOOTH movement. You should be able to wipe out most of the old grease but use BRAKE SPECIFIC grease in those boots and on those bolts. They should slide nice and easy..
Should you, for what ever reason, remove the aluminum bracket (part #10) the calper bolts to, it has an ALIGNMENT SLOT that MUST be aligned with the swing arm or you will destroy that bracket.
2006 Yamaha FZ-6 (FZS6V) Rear Brake Caliper | Babbitts Online
Duble click on the pic to enlarge;