First, I can see conveyor belt on both exits in your screenshot.
Also, are you sure your intention was to change loaders ON THAT PARKING ?
The loader option in the scenery customization page it's supposed to tell the sim to use a certain kind of loader ON THAT PARKING ONLY. If this is what you wanted to do, that's fine. But if you wanted to change to belt loaders for that kind of airplane, everywhere, the right place would be the airplane configuration editor, which will set which loaders will be used on that airplane, everywhere, by default. Unless, of course, a scenery customization for a specific parking would tell otherwise.
