Mazda P5 rear brake pad removal
See post #3 and review page 4-11-23 in the service manual.
Here are some pictures that may help you locate and remove the rear brake pads on the Protege5.
1) Here is a picture of the bolt that must be removed to access another allen head screw that can retract the piston for brake pad removal and installation.
2) Once the bolt is removed, use a allen head screw to retract the piston.
Hope this helps.
Note: you do not need a C-clamp for changing the rear pads. For the front pads, you could use a C-clamp to retract the piston.
As always, make sure you do not have too much brake fluid in your system when each piston is retracted. The brake fluid can overflow in the brake reservoir bottle in the engine compartment. Extract fluid as necessary to not overflow the reservoir bottle.