Nick - certainly unwarranted 'fiddling' (ie pushing) during take-off is known to be potentially hazardous (see Boeing paper). I can see no problem with a similar over or undershoot of N1 in a g/a where performance is slightly less critical. As to any mechanical effects, it is the clutch that is being over-ridden, and I don't think that would cause a problem. I personally go with Tee-emm's last paragraph.