These bolts are far from plastic deformation.
They operate well in the elastic range, which means they will revert to original size when released.
There has been numerous discussions from all walks of life, especially on the stretch bolts for the 1.8.
I have found and referred to an article by the company that designed the bolts for the 1.8, and the head man there said that they can be re-used a number of times.
http://www.boltscience.com/pages/glo...ingarticle.htm
I think you should ask if ANYONE has had any problems re-using these bolts. I have re-used them, with no problems. As a matter of fact, I have never had a problem with any critical bolts on any engine I have built. I have some threads come out of aluminium blocks on Rovers, but I suspect our hamfisted "technicians" in this country have got a fairly flexible view to applied torque, so the damage was most likely done before I arrived on the scene!!
In some cases "re-use" by Rover is synonymous with "we have used some compound on the bolt, but we don't want to tell you" thus "buy new".
Does not make a lot of sense to a private chap trying to keep his vehicle on the road, does it?