In theory you should be entitled to access. However, in practice it will be up to the interpretation of the lounge agent of the day. I have found some QF agents in Australia are now reluctant to change FF numbers/programs on a flight where the boarding pass is already issued, trying to prevent people using one membership for lounge access and then changing to another for flight credit. But I have not ready anything on QFF or AAdvantage program terms and conditions that addresses this scenario. My gut feeling is that you are more likely to have success in the USA by showing a QFF card along with your boarding pass than you would in Australia. I would normally hand over the baording pass and QFF card together and make a comment such as "Here is my Qantas membership card for lounge access, but I am crediting this flight to my AAdvantage account because your programs is much better than the Qantas program and I don't need any more Qantas points at the moment."
Note that Admirals Club is a separate program to AAdvantage and the AAdmirals Club staff are generally much less concerned about which program your flight is crediting to than Qantas lounge staff seem to be.
But as I noted initially, there is no guarantee and no program rule you can point to that provides definitive ruling on status-based access when crediting to a different program.