I assume your talking about making L2 - Passenger Door 2 ((L;PassDoor2,bool) in the CS code) the MAIN EXIT? Although not familiar with AES or FSPax I would tend to agree a lot of airlines don't like cattle class passengers tripping through 1st and Business diverting them right through L2 or using dual Airways.

I had a bit of a play with it and all I can come up with, in the short term, is making both doors open and close simultaneously using the MAIN DOOR Animation Control Icon --- which is basically nothing!

I get the feeling your utilities require the (A:EXIT OPEN,bool) tag to equal 1 and that can only be set if the MAIN DOOR is open by the (>K:TOGGLE_AIRCRAFT_EXIT) command which CS has tagged as L1.

I'm thinking the only way to do this is in the mdl file which we, mere mortals, cannot edit.  :-[