The head bolts on any engine should be torqued to factory specs that are well below the yield point, i.e. the point at which they permanently stretch, so follow the engine specs and put your mind at ease.
Bolts behave essentially like springs: you can stretch them up to a point and they will return to the same length as many times as you want, but if you pass a certain point (yield point) they will take a permanent set, as a spring would. All manufacturers specify a certain torque that should not be exceeded; if you do that you will be OK.