1- Backup Retail Game save using
NTR CFW, Gateway backup DON'T WORK !!!
2- Create a new save in Gateway Mode with the ROM version.
3- Copy .sav file on 3DS SD and rename it to
000400000FF40A00.sav to avoid SDF bug.
4- In Gateway Mode, enable game ROM with multi-menu then launch
SaveDataFiler.
5- Export CTR save then connect 3DS SD to PC and overwrite SDF backup files with NTR backup files.
6- Now
DELETE both ROM .sav file and
000400000FF40A00.sav.
7- Back in Gateway Mode, use SDF to import ROM game save to
CTR.
8- Now copy newly created
000400000FF40A00.sav and rename copy to ROM save file.
9- Done