Okay, I'll give it a shot. It looks like my extdata is 0000008f, right? https://www.3dbrew.org/wiki/Extdata
If this doesn't work I can try messing around with SDF tomorrow I guess, or renaming my Nintendo 3DS folder like you suggested.
If you are in the US, then yes.
And don't panic if you rename your Nintendo 3DS folder, I did that too when I downgraded to 2.1, and when I updated, I deleted the newly created Nintendo 3DS folder, and renamed the renamed one back to Nintendo 3DS, and I still have all my games with all the saves (3DS/DSi/GBA)