I'd recommend keeping the status FFP number in the reservation up to the point you leave the lounge. Get the team to change it over then, and if you feel paranoid about losing a good seat, get them to put a note in your PNR stating you have BA Gold, OW Emerald...whatever. That SHOULD prevent any problems. Make sure you get a re-printed boarding pass.
I've done this when op-upgr*ded - and didn't then loose the upgr*de so I am confident it works!
[This message has been edited by Swanhunter (edited 09-10-2003).]