Example: The FSL A320 will NEVER use Cargo Loaders. They will always use conveyors.
And why is that ? Real life A320 has its own dedicated ULD, called AKH, which is how we configured it by default in GSX, on the rear door. Here's an A320 at Zurich loading it:
Instead of customizing on a gate by gate basis I want to always set only belt loaders and no rear stairs to everything related to the 320.
If you REALLY don't like the AKH container (which is used ONLY by A320, it has been designed for it...), there's no need of course to configure it by-parking. The choice of a container on a parking should be done ONLY in extreme cases, where you KNOW the parking is too small for the larger Cargo loader to maneuver.
But the normal choice of any particular kind of loader or container, if you don't like the GSX default choice, would be using the AIRCRAFT Configuration page, which does exactly what you asked: change the aircraft configuration, regardless of the airport. GSX has been like this since it was released...