This is how I understand it works. Basically the owner of the record should propagate down any FF changes, but any other carrier, if you manipulate just that carrier's info, should not propagate back up.

So I would try giving US your US FF info and deal with them as you normally would.

Then use the CO record at co.com and make sure your CO number is still there (if not, put it back), and do what you need to there.

Good luck!