I seriously doubt it will go that far. But I offer the following recommendations:

1. When you remove the headbolts, run a good, clean 7/16"-14 UNC tap all the
way down the holes and then clean the tap each time you do it so you don't
get the stuff back in there.
2. Before you reinstall the headbolts, clean the threads and the pressure
surface under the bolt head with a wire wheel to remove dirt, rust, etc.
3. As you reinstall each headbolt, put a little clean grease on the threads
and the pressure surface so that the torque you apply goes into increasing the
clamping force, not just twisting the bolt shank and overcoming friction.
4. Torque according to the manual, starting at the center and going in a spiral
and do it in 3 stages: 29 ft-lb, 58 ft-lb and finally to 65 ft-lb. All bolts
should screw in smoothly. If you feel roughnes or jerkiness go back to #1
above, at least for the affected bolt.

In almost 40 years of working on Volvos I have only broken one headbolt and
that was because the threads were not clean and smooth. (It came out easily.)
I have NEVER bought new headbolts.

--
George Downs Bartlesville, Heart of the USA!