With the Aircraft Master Arm module it is possible to change the pylon loadout of aircrafts by using predefined "pylon loadouts".
While extremely helpful, however the pylons configurations are always limited to ONLY predefined loadouts. And this system could be improved by a lot if the players were able to customize each and every single pylon individually, and perhaps even save their custom pylon loadouts.
Just use the Aircraft Master Arm module on an aircraft, you will be able to change your pylon loadout only to and from pre-defined pylon loadouts.
My only concearn with players being able to configure each pylon individually is that CAS aircraft could become too extremely powerful, since people already complain that CAS is too powerful in the mission Mike Force. But perhaps this could be balanced out by adding customizable limitations to how much of each ordnance certain vehicles can carry, since without any limitations a single F-4 Phantom would be able to carry up to 285x Hydra 70mm rockets + 4x AIM-9 Sidewinder + 4x AIM-7 Sparrow!