It is called a hex editor, you can use 3DSExplorer to rip the individual save blobs from the save file to work on.
3DSExplorer: http://code.google.com/p/3dsexplorer/
I put some info on picking apart a zelda 3DS save a while back before 3DSExplorer was made.
So would you be interested in looking at the decrypted save files I posted from a 128k r4 save and a gateway .sav and seeing what you can deduce? I will have to try opening them both with the 3DSExplorer to see what that produces, but having someone look at them that has some familiarity with the layout of the 128k save might help us find a way to cut and paste one save into another...maybe with the 3dsexplorer?









