Check this months Welding Journal - Sperko article. I believe this is addressed in there.
EDIT: What I mean is I believe the topic is loosely addressed. Obviously, as Marty indicates, a stop welding / stop work must be made while a new PQR is run and subsequently tested, approved and a revised WPS is authorized. If the new PQR is run with the EXACT same variables as the original PQR and the only change is impact testing is added, I believe dispositioning an NCR should be a no-brainer. If impacts fail well then you know what will likely hit the proverbial fan... could see all kinds of after effects... hardness testing of welds, etc.,
Take a look at QW-401.3 and see if it doesn't give you some guidance?