You can read more about this tool, how it works, and why I created it on my blog.
This repository contains a NDS homebrew tool I made for myself to help me transfer my The Legend of Zelda: The Minish Cap save game from a counterfeit cart I purchased by mistake to a legitimate cart I bought after the matter. The tool is only capable of backing up SRAM saves, without making any checks as to whether the game supports SRAM saves. It will not backup a game ROM nor will it restore saves.
I've also included a tool for unshuffling EEPROM saves, similar to the VBS one that comes with Rudolph's GBA Backup Tool.