1999.5 Golf rear brakes - do I need a caliper tool?

Hello group.

Apparently I need new rear rotors - corrosion is getting pretty bad, and
actually spreading down the rotor where the pad doesn't touch, and they are
slightly warped I believe... The pads were done at 60K Kms (car has 109K Kms
now) and have plenty of life on them, but I know they need to be changed if
I get new rotors.

Friend of mine who did my fronts said I don't need special tools to do the
rear rotors, I seem to recall needing a special retractor tool to push/turn
the pistons back into the calipers on the rear brakes on VW's.

I'd like to install Zimmerman rotors and PBR pads like I have up front (done
at around 90K Kms just before this summer), and do them myself - as I like
the way the front brakes improved when I changed from stock.