I'd like to request that the feature be modified to allow users to select their own registrations. Otherwise, it's no different than (and just as useless as) the aircraft ID.
The point of a reg number system should be to organize (and semi-realistically) define an airline's fleet, in the case of US airlines, using the airline's preferred suffixes (AA, AN, US, UW, PS, UA, etc.) If it's just a sequentially-assigned letter-number group, it's meaningless to the aircraft owner, and will result in the person having a fleet full of randomly-registered aircraft whose reg numbers bear no relationship whatsoever to any logical rhyme or reason.
As it is, I'll simply ignore the AM-assigned registration number and continue to create my own, using the aircraft name tool.