Ok so can you , or should i say would you re-use stretch bolts for the head
Old old mate says he has always re-used with no problems 
Hes an idiot then
Years and years ago, when headgasets were copper and heads iron, the heads werwe often held on with monster studs or bolts, these could be re-used adn often required re-torquing after a number of miles.
Now we have alloy heads and composite or multilayer metal gaskets.
These use a high tensile bolt which is angle tightened to the point where they 'yield', at this stage they actualy go to a stage where they are elastic and apply a sprung clamping force.
The benefit is that it maintains a constant pressure to the gasket across the full temperature range and does not require re-tightening.
They cant be re-used as once they have passed the point of yield they cant be re-tightened to achieve the same.
So, in summary, old setup means re-torquiing (a git of a job on a OHC setup) after a number of miles and a compromised clamping force on the gasket. New setup means fit once and forget plus a better more consistent clamping force.