All you have to worry about is getting it to retract.. once you're done it'll take a few pumps or more to push the piston out.
To get it back in, the universal method is to get something like a large c-clamp so that you could apply compression on the piston... then you need to crack the bleeder valve...
If that doesn't work,
On my VW i had rear discs, those pistons needed to be screwed back in.. they had an allen/torx/elongated opening to allow fitment of a tool to turn the piston(look for that).. also need to crack bleeder on that as well. But i'm pretty sure the twist action was only necessary since it had an e-brake function inside.
Alright, just got a fresh look at the haynes manual.. on 90+ models it suggest putting the caliper on the disc (without pads) and using a screwdriver through the inspection hole to leverage the piston in... how retarded is that...
i guess on pre 90 a c-clamp can work, and they also show a picture of doing this while the caliper is on the disc.. i usually try to do this off the disc.. I'm unsure if the caliper is bolted down at any of these steps...
gah i need a real manual.
'92 YJ, 4.0L, rs5000, bds 2", 30" for now.