Simpler factory reset on the NST is to hold the two lower page turn buttons right after switching the device on, keep holding them until you get the confirmation screen asking if you want to reset. Also, I've deregistered, re-registered, rooted, unrooted and rerooted my devices numerous times without a problem. Usually you just deregister the device, reset it to stock, Instead of letting B&N do it I install my backup with Nook manager to return to stock and reroot away!
OB