MAN was a rumour, but I think it was started by some guys who wanted a MAN base
You could always take the Command in FR & defer NAS for 18mths to join as DEC instead ? we "should" be recruiting DEC's for the foreseeable. . . of course, the policy could change & I would then regret giving you that advice.
I know guys who were offered the position, turned it down, and were welcome 6mths later when they realised they had backed the wrong horse. Unlike some other companies, they seem wiling to accept they are not the only show in town , and should you decide otherwise it is not held against you (I have heard the inverse about NAS long-haul however)
Certainly if you come along for assessment, and it is going OK, there would be no harm in instigating a frank discussion on staying with FR & gaining Command versus how long (?) to have a crack at it as a Contractor in NAS. They are normally quite amenable to answering these concerns, & realise you have your own life/career to run whether they are included or not.