Okay, so tonight my venue is doing NML month 6 and I'm using a batman family team. I was wondering if between games I switch the belt user (First game Omega batman uses it then say next game Hush Wayne prime uses it) is that legal?

Officially, no.

Assign: Utility Belt is assigned to a character when you build your force and only that character can use its effects. When the assigned character is KO'd, opponent scores Utility Belt.

You only build your force, well, when you build it. You don't rebuild it after each match.

Of course, your venue might have house rules, so you could always ask your judge.

Alrighty, thank you.