They are good for a few gaskets and there are length criteria for stretched (bad) bolts but I doubt yours are that far gone. As for retorquing, I think it is recommended by performance experts (Unitek) that the engine should be run at temperature and each bolt should be re-tightened to full torque. You will see that the bolts seat a bit further with each re-torque and I think MA recommends a cycle or three of tightening. I have done them both ways and also had a good result without re-tightening if you follow the Volvo staged tightening protocol.