Since they've cancelled ARN-ORD, resulting in them having to transfer everyone to the CPH-ORD flight, I would not be surprised if they'd already done some of the upgrades in the system before you even arrive in CDG. If so, the check-in agent might just get a message from the system to upgrade you. I have been told that this happens from time to time. The question is, of course, whether or not you will be one of the lucky ones, but as an EBG you have the highest priority, barring any EBPs, that is...