No need to make so many threads.
Anyway region conversion for saves is ever the fun topic.
The GBA has no overarching save format like some later systems where you might have user profiles and whatnot. Basically all random data however the devs chose to do it.
Sometimes they will work just by renaming the file.
Sometimes they might have a minor difference, I can see some kind of indicator/ID value being a thing but I have not seen it in the wild. Granted most people either restart a game, use cheats or use the other region's ROM so I don't imagine it comes up very often (we used to see it more on the DS when things would come out in Japan early and everybody and their donkey would have flash carts to play with).
Mind you the start value of many saves is some kind of serial (need not be the same serial as the header though) and I guess a game could check to see if it matches there first of all. Might not even include it in the checksum. You might try copying the first however* many bytes of a game and seeing if that counts.
*how many is the big question. It could be between 2 and 200 though likely on the shorter end. Without delving into the game code I would likely start two games, if it is the sort of game that allows you to select a character (thinking something like pokemon where you have a choice of sex, name, avatar...), save as soon as possible and compare, and compare against a far later save, and compare against a same options and soon as possible save between regions. Not flawless but seeing what is common in those is likely a good bet for a candidate here.
Sometimes the differences might be more fiddly. For instance Japanese games might use a different text format and thus need any user names changed, and presumably a way to bypass any checksums/hashes the game does for the save (either learn the method it uses for that game or hack the game to ignore it).
Other times the differences are radical (sections different sizes, different locations, different order, extra data...), or radical enough that the 30 hours you spend figuring out the format (other than extra data all the previous stuff is 10 seconds with a slow program to sort once you know what things went where and how they changed) is still less than the time to replay to the point you were at.
