Maybe it'd just be best to link every firing option in the historical manner...
All .50s firing with just primary trigger, for US planes...
Primary trigger firing the inboard cannons and cowl guns, secondary trigger firing outerwing armament for 190s..
Primary trigger firing cowl guns for 109s, secondary cannons, gondolas will be "switched ON" like any other ordnance with the use of the backspace key, so will be fired with the secondary trigger when it is ON...
... historicity and consistency.. only price we have to pay being having to hear whines for about a month until the guys used to arbitrary AH depiction finally just adapt to it...