It looks like you want to extract the Cabinet from a rig into another rig. You could load that rig and extract the Cabinet with Drag&Drop from the Cab module, so you have it as Cabinet preset. Then you can just Drag&Drop it onto the Cab section.
Unfortunately, the "Cabinet From Rig" functionality is not in the editor, yet. I agree that just dropping Rigs onto the Cab section would make things easier.