This discussion really belongs in the CO or US forum but to ensure completeness...
Originally Posted by
luv2ctheworld
Welcome to FT!
You'll be stuck with your US *A Gold status; it's not "transferable" or mappable to CO. However, if you are trying to merely gain access to the elite check-in line, there shouldn't be any reason why you can't flash your *G from US to get in CO's line (well, I don't think there is any, except the ire of actual CO elites).
True. Though CO has great online checkin and kiosks at the airport, so there is no need to stand in line unless you skip the skycap and check luggage or have other special needs.
Originally Posted by
luv2ctheworld
Early boarding is tough because your boarding group is based on your FF number. If you use your US number during online booking or online checkin, you will get priority due to *A, but you won't get credited the miles to CO, obviously. And if you put in CO, you won't be able to get the priority boarding.
Not really accurate IME. I have no CO status and had no trouble boarding with the elite group. I had my old expired

UA *G card but the GA didn't even look at it (gotta find my current card)
Originally Posted by
luv2ctheworld
A potential solution, not that I condone this or that it would work, is to first print out your BP at home with your US FF number, then at the gate, ask the GA to switch to your CO number (assuming you want credit on CO) before boarding. Then when it's time to board, use your online BP while keeping your CO BP for later mileage verification if necessary. Again, not that this is "ethical" or would even work, but it's a solution. One hiccup could be that your onlnine BP would be invalid after the GA prints a new BP.
This is totally unnecessary based on my experience. Also if you accidentally get miles credited to the wrong program it will be hard to fix.
From what I can tell, if you are *G in the *A program, the main things you will miss (without CO status match) is ability to pre-reserve certain seats (though many have reported success doing so anyway via call center), potential free upgrades on certain fares and bonus RDMs. On the plus side, se I got bonus EQMs from CO which I don't think I would have received from UA.