Re torqueing head studs/bolts

The reason to break them and then re-torque is that an accurate torque reading can only be made while the bolt/nut is moving. You can't get an accurate reading without it moving.

I have pretty much re-checked head bolt torque on every engine after a few heat cycles for 4 decades. But I don't loosen and re-torque anymore; I just take the torque a bit beyond the spec to see if the bolt/nut moves and it not, it's good. Just looking for loosened bolts/nuts or gaskets that have flowed or settled, and they seem to show up that way.