What do you mean what if it had its original valid ID? Then it would likely register but then either that ID will be allowed to affiliate to the talkgroup or not.
I don't know why a tech would program a legitimate subscriber for NAS, that's a horrible idea for a legitimate user and makes no sense. There is already an option for disabling its ability to make a call on the talkgroup with TG/AG Disabled but still allowed to affiliate to a talkgroup for monitoring purposes. That is the legitimate way Motorola allows for such a situation with a legitimate radio. Then, there is a lot of FD guys here have a unication pager, they can receive their page and then flip to the trunked system to monitor until they get to their station. It only works well because the system is simulcast with 1 site so it there is no other roaming and missing transmissions
With the availability of cheap XTS radios, my signature is no joke. I thought the systems around me wouldn't be such a hot target. But every once in a while logging, it will come up - REFUSED UNIT REGISTRATION - UNIT ID: 1. Link Layer Authentication can't come soon enough when they start stealing legitimate IDs