It's about the same as changing a timing belt - see volvospeed/bay13. Of course you will drain all the coolant first. I found I could loosen the 7 pump bolts pretty easily but I couldn't work the pump free until I removed the timing belt idler. It took a little patience to make sure the mounting surface on the engine block was really free of old gasket material. I used a pump from the Volvo dealer which came with new bolts (they were pretreated with some anti-seize or similar substance on the threads).

There may be aftermarket pumps that are ok. For a different car (a Ford, not a Volvo) I bought an aftermarket pump supplied by Bosch at half the OEM price - it was ok but not as substantial as the original one. I would usually choose the factory part for a car I planned to keep a long while.

I wouldn't want to second-guess you - are you sure it's not just the hose that runs behind there to the reservoir?