ROM Hack Question - rebuilding a romFS and exeFS into a .3ds rom

[Halvorsen]

I've been searching all over for around two hours now and can't find a clear answer.
I have Smash, and I have my exefs and romfs ready to pack.
I tried HackingToolKit, but literally any option gets an error, "(x) cannot find the path specified.
After this, basically everything that came up was how to use the game in HANS (which is working perfect btw), or SaltySD.
Nothing on how to rebuild my romfs and exefs back into a .3ds.
Help?

 

[Halvorsen]

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[evandixon]

Try 3DS Builder. In any case, you'll need an Exheader too.

 

[Halvorsen]

Where should I get the exheader? I'm sure Braindump doesn't extract it, so is it possible to extract it from a full .cia file? If that's a thing in 3DSBuilder, never mind.

 

[Jiro2]

I've had a similar question, from the Fire Emblem Awakening SSM patch thread. I want to apply the patch to a .3ds file (and possibly modify the patch). In order to do this, I must convert the .3ds file into a romfs, put the patched files in the romfs, and convert it back to a .3ds.

No guide anywhere explains how to do this, although there are instructions which explain how to use it with HANS (which is not what I'm trying to do.) Can anyone point me to something useful?