Easiest way would be to make an xdelta patch with xdelta ui for the rebuilt romfs.bin against the original decrypted one, should end up less than 200 meg.I just replaced the english voices with the japanese voices yesterday.
Till now, it works really fine.
If someone could tell me how I can create a "Patch" the doesn't contain a rom (3ds, cia), I could upload it. Otherwise... no
You could probably do scene rom against your own but that could end up insanely large depending on how similar the actual rom ends up to the scene one.
A tutorial or more details in general would be great regardless.Only renaming is not enough.
When I'm home, I could write a Little tutorial for it