Ref what if RA Climb is issued when already at max FL.
Although I'm not an avionics engineer but I did occassionally whitnessed TCAS programming (because most or all TCAS processor units are out-of-box devices they need to be programmed after installation to particluar airframe to reflect actual indicators/controllers/transponders/etc config). One of the settings should be entered at programming stage there is AIRCRAFT MAX FL. Normally it would be the max certified FL. As I was told by engineers, this setting is to prevent TCAS to issue RA Climb when aircraft is already at max FL. So I believe this answers the question in general, however TCAS knows nothing about real time FL limitations due to weight or temperature.