Almost ready to bed the rears. Huge pain figuring out the piston, lots of youtube videos with info that just didn't work. Rough recipe:
(retract EPB with vcds/obd11 first)
remove guide pin boots, then remove caliper guide pins.
remove rattle clip, slide caliper off, remove pads. secure caliper.
I took the carrier off (after removing m14 triple square bolts), though I saw someone remove the rotor without taking it off.
Replace rotor/set screw. Reinstall carrier with fresh bolts. hand-tighten to make sure it's straight.
Open up brake fluid cap.
Use the twisting piston retracting tool (I used metalnerd mn3272). Twist
clockwise until there's an obvious stop.
Then, use a normal piston spreader to push the piston the last bit of the way. I wasn't able to clear the new pads without doing this.
Close brake fluid cap, grease up pistons, install, and then slide caliper back on and grease/thread guide pins back on. Reinstall rattle clip.
Torque everything down, reinstall pin boots and run the EPB close setting.
Dunno if he's around anymore, but thanks
@Cliff for the hookup on the pads and dropping a comment a couple years back about the piston retraction process.