Hi
Never understood Haynes on the rear calipers saying do not touch. I stripped mine completely and rebuilt and they have worked faultlessly, even using the original pistons. As to the front ones they are pretty easy, the real pain is getting the retaining spring out which sits halfway down the bore. I found poking one of my dental tools through one of the two drilling’s from yhe outside helps to lift it out of its groove, then using another dental tool to gently encourage it out the rest of the way, being careful not to make a mess of the bore.
The real pain is reassembling the handbrake mechanism on the rear ones, that was a challenge which I seem to remember using the hydraulic press to hold part of it down whilst I aligned everything. I have that joy to revisit when I rebuild mine which are all cleaned ready to go back together.
Peter