Hi! I just want to deeply thank Bomborolo for editing and sharing the savegame. It's actually the only edited savegame I found on the internet.
I managed to get this on my legit Tecmo Bowl Kickoff cardridge so I can play on the 3DS
First I had to convert and rename the savegame into a format which my flashcart accepts using a converter ( http://aspspider.info/uniquegeeks/nds.aspx -> from desmume to X - Supercard in my case).
Then, after putting it on the Flashcart in the same folder as the ROM, I could load the edited game on my DS Lite.
After that, I connected the DS Lite with my 3DS with the original game in Wireless multiplayer mode and trade the teams.
Now I will play Tecmo Bowl Kickoff with both machines and a friend in multiplayer until the Superbowl