Yes, all the manuals tell you to use new bolts (i.e., those bought from your local Volvo parts counter). Unless the threads are suspiciously defective, I just smear on some blue (medium strength) LockTite -- I've noticed that original bolts all show signs of having originally been coated with the red variety, but that's "permanent" or high-strength, isn't it? I prefer blue so I know I can remove them (for the next set of rotors) easily -- I'm not afraid of them getting loose with blue. Your decision, though.
Good luck.

By the way, I remember that you need a thin wrench for the rear caliper bolts -- as I recall, there's no room for a socket, though I can't remember why -- so check to see that you have a wrench that will fit on the bolts before you get started.