source system (cfw)
1. freeshop sudoku into source system
2. inject old sudoku srl/nds into freeshop sudoku and hax save as well
3. export and import the injected sudoku
4. test it and make sure it boots b9sTool
5. copy the exported injected sudoku (4b344445.bin) to somewhere for safekeeping
6. nand backup this system

System tranfer source -> target. don't worry about freeshop sudoku not transferring.
the moveable sed being transferred is what's important

target system (stock firmware)
1. buy sudoku from eShop
2. place 4b344445.bin in Nintendo 3DS/<32 digit hex>/<32 digit hex>/Nintendo DSiware/
3. in system settings, import sudoku from SD
4. boot it and dsiwarehax should work