ROM Hack Easiest way to build a .3DS ROM?

[DarkFlare69]

I would like to take the current .3DS ROM I have, and then decrypt it to get a romfs folder. Then, I would like to overwrite a file inside the romfs folder. I can do all this, but I can't manage to rebuild the ROM into a .3DS no matter what I do. I've downloaded some tools from DSHack.org, and they don't work. Someone please link me to a tutorial and downloads.

Thanks, it would be greatly appreciated.