Many, if not most, states already have Such a legally defined status, called the “unorganized Militia” in Maryland. MD does not keep a list, ‘tho’; that would be called an “Enrolled Militia”, and there hasn’t been one here since the Civil War.
Alas, membership in the militia, unorganized or organized (MDARNG, MDANG, MDNaval Militia, or MDDF) does not confer any
exemption to Maryland’s onerous anti-gun laws.
But I agree, creation of an enrolled militia force, with full exemption from ‘Gun-control Laws’, including the 1937 NFA, the 1969 GCA, and so on, would be a good thing for the Country, which is why we shall never see it.
It would via the 2nd Amendment.