Are you saying that you and I are not both Presbyterians, for instance, and that American who confess what they call the Wesminster Confession of Faith should call their Confession something else?
If I believe in the establishment principle and you don't then obviously we are Presbyterians who differ on the subject. If my confession maintains the establishment principle and yours doesn't then obviously our confessions are different and shouldn't be called by the same name. The point at which your confession differs from mine was not written by the Westminster Assembly of divines, and therefore should not be falsely respresented as their work.