I am a first timer for do it yourself brake pad replacement. Had no problem with the fronts but rears are giving me fits. i understand the rear piston rotates into the caliper instead of just pushing in like the fronts. Any tips on how to get the rears piston in far enough so I have clearance to get new pads on rotor?

 

These two threads should be of help
https://www.rx8club.com/series-i-tech-garage-22/tool-push-rear-brake-caliper-cylinders-72878/
https://www.rx8club.com/series-i-do-yourself-forum-73/diy-brake-pad-replacement-68073/

Not only do you have to screw in the rear piston, there is a small tab on the rear of the pad that needs to slide into the grove of the rear piston. Try making small turns to the piston the align the grove wit the tab.