If replacing only the rear pads on a W124 300TE, one does not need to remove the caliper. Use a long pry tool or caliper tool to press the pistons back in, one a a time. I did mine on my 300TE a few weeks ago, and changed the brake fluid.

If replacing the rear rotors as well, then yes caliper comes off, but no the parking brake can not be engaged for the obvious reason.