Originally Posted by
atflyer
Sure, but it all depends on how long the layover is and how badly OP wants to see Paris. If it is a layover of 8-10 hours.....then the 1.5 hours RER return plus 2 hours entering and leaving the airport may be worth it. Did something similar during a long stop in Shanghai which was ok - and a next time I felt more like sitting it out relaxing in some snooze corner. BP may not work for a 2nd time entering the lounge (although I would say AF should not care about this - OP will in fact spent less time in the lounge overall if heading for Paris), but I never experienced problems in leaving & entering an airport in such situations (one ticket, all BPs printed, leaving the airport for some hotel or city visit during a long layover).
Boarding pass could be an issue because at CDG while transiting the boarding pass is scanned by security. I am not sure if CDG does this, but at some airports once you have scanned a boarding pass to get into the secure area, re-scanning will lead to an error.
Some years before the pandemic, I did something like what the OP wants to do at 2G. My companion forgot a backup battery in their checked luggage. So we exited, the bags were brought out, and then checked back in. If my (poor) memory serves correctly, we didn't get new boarding passes. We were able to reuse those that we had with us. If that's still the case, then the OP will have no issues exiting after the boarding pass is scanned in transit, and then re-entering using the same boarding pass.