While your assessment may be vaguely correct ... other (more significant) concerns are raised!
Was your friend not fitted to these shafts? If so, why is he now considering changing the length? The irons lie angles may need to be evaluated as well! Its not as simple as cutting down a driver shaft ... time to see a good club-fitter
How much stiffer a shaft gets after tipping the shaft 1" depends on the shafts properties ; different types of shafts react differently