Seeing how savegames are not stored on the cartridges anymore, I don't see how it could be possible.
Part of using a modified savegame, required some way to modify the save in the first place. I.e on a already modified device or on hardware like Powersaves. Then you could put the cart with the modified save into "any" 3DS.
Edit: I'm guessing I am missing the point here, and making a fool of myself.