I don't know exactly how they do it but I imagine since you registered your radio and they know you have the DMR key through your registration and the electronic serial number, they probably will be able to check and just put that back on the radio if it gets wiped off?I'm also guessing that this would be something they automatically check, if they need to, prior to wiping the radio clean.
Before Paul Opitz, UPman or the guy responsible for us having the SDS scanners, passed away earlier this year, he had told me that the registration key was useless for anything once you put it in the scanner. He said there was absolutely no reason to save it and it wouldn't do you any good even if you did because there was no use for it. Since that registration number goes with your scanner and it's ESN number, there's no way to use it on any other radio and Uniden would have a record of it. Even if you bought it and had some company add it for a small cost, it's still only good with your radio's ESN. So through that ESN number I'm guessing they can tell that you had the DMR key?
Like I said, I'm not exactly sure how it works but Paul was very clear that that number could never be used again once it was used the first time and saving it was pointless.
Brian (COMMSCAN)