Yea I figured it would be a lot of work. Jw though, could you use Pokemon essentials information to add them? I'm not sure if you know what that is but basically it contains a (I think) a pmb file with every Pokemon name,base stats,moves able to learn, evolutions and everything else. There's also a folder with all the sprites of them forward and the backs . So could you use that to edit the past games?
Sorry I just don't know how to edit games yet. I have game maker and rpg maker. And I'm able to create a Pokemon advance game and add all 649 Pokemon in there. I didn't know if it could work the same for a ds rom.
I'm working backwards from gen 5 to gen 3. I really wanted to take my serperior with me like ash does with his Pikachu.