The rules .CFG files in the Addon Manager\Texture folder are shared between MSFS and P3D, but the Simobject folders aren't.
This means, if you just want to change rules for operators that already exists, it's fairly easy to do.
However, adding a new operator in MSFS is more complex than it was in P3D, because in addition of just adding the objects and creating all the various texture folders, you'll also need to convert the texture from .PNG to .DDS and adding all the various flags required by the package, and add all the new files to the package .JSON file, and all of this is normally done by the SDK package builder, which needs to start from the project source files.
If your rules are related to a real world operator that is missing from GSX, it would be way better if you just said what it is and where it should operate, and we can add it very easily, since we have a fully automated procedure to do that, which integrates with building from the source files.