I managed to restore it using Tinfoil.
auto
This is my save from the Ancient Ruins which is after finishing Catfish Maw.
Unzip to the root of your SD card, and use Tinfoil to restore.
I've tried loading some games requiring 3.0.2 like Steamworld Dig 2 and Penny Punching Princess, and they do launch. So I guess I've answered my own question.
Hey, great tutorial. It has worked for me however, I was on official firmware 3.0.1 and referred to gbatemp.net /threads / list-games-required-firmware-version.485959/ to get a list of games that match my stock firmware. From this list, I chose "Cartoon Network: Battle Crashers", and...