“can form and call themselves “Boy Scouts of America””
They’d want to use a different name.
Be specific: what do I say that makes no sense to you?
You’re implying that a group which is a member of a national organization can make their own rules, independent of the larger organization. That is antithetical to the reason for “grouping” in the first place.
But you are right, they would have to use a different name. In other words, they would no long be a unit of the Boy Scouts of America.