I don't mean copying it down to every single thing; basically edit the sprites, storyline/events, dungeons, items, moves, and pokemon. I'd keep the gameplay the same as EoS because GtI's gameplay was terrible (no healing during any weather is complete bull for example). That, and maybe add on to the story so it's longer and complex.
Might it be possible to edit GtI's view in the dungeon? Like make it the same size as the previous games (not all zoomed in in other words so you can see the dungeon layout better)? And perhaps edit the models so they have unique idle animations?