Originally Posted by sbm12

AA and UA are in different terminals so you're not likely to have access to the UA club upon returning to the airport. I'm not even sure that you'll get access en route as you typically need to clear security to get back in to the transit area.

If you were in that terminal the whole time it would probably work in your favor as NRT is a station which stamps the BP to show that access is permitted and returning to the club with a stamped BP generally gets one in without further credential verification.