For one thing, Raoul, there are already UN statutes and treaties regarding the moon, et al.

The 1967 UN treaty for one.

However! If there were [hypothetically] a self-sustaining colony on the moon in the year 2076 of maybe 10,000 inhabitants,
[I'd be a hell of an old man in 2076] and if those 10,000 people
decided to declare themselves a lunar nation, claiming the moon as their own, in violation of the 1967 space treaty.
How the hell would the UN enforce the 1967 space treaty without
a punative armed-force in space?
Even if the UN tried to enforce that treaty with such an armed-force,
should it exist, it may encounter resistance reminiscent of the American colonists in 1775.

Jacob