7M head bolts can be reused but hardest part is to clean out the splines so that the spline socket goes fully into the bolt head. Even with the stock bolt torque the spline socket twists and it always looked to me that the standard torque was the at the limit of my socket. Also note the factory manual gives an unbolting sequence as well as a tightening sequence - I presume because the head is so long. Issue with 7M bolts is that they lose torque after a head gasket change. The manual doesn't mention it but other vehicle manufacturers can recommend to retorque head bolts. The service interval for valve adjustment for a Peugeot I owned was every 12,000 miles and the head bolts were to be retorqued before adjusting the valve clearances.