[Enright]

I would have thought that freeing off sticking calipers would be easier than changing for new ones. Like Ritchy experienced, the carrier bolts rarely get moved so can be an absolute swine to get off. Then there's the hassle of getting the handbrake cables out of the way without damaging them, and bleeding the new calipers afterwards.
The only things that can really stick are the sliding pins (usually easily rectified) or the piston itself, and if you can get the caliper clear of the disc then a stamp on the pedal should budge it. After that you just need to wind it in and out a couple of times, and perhaps spray some WD40 up under the piston seal.