Not sure if you need to erase the eeprom from the node. As the key is stored within the encryption chip when you sign it - this is somewhat of a guess, based upon my understanding of signing.
Erasing the GW eeprom wouldn't be a bad idea. Because that's where the administration probably is stored. As far as I know other nodes are not influenced event when they are repeaters. As repeaters don't even know wetter the other nodes are signed.
Hope my 50 cents help out.