ROM Hack Sound files help

[wiibomb]

Hello there, I made this thread as a final resort about how should this work.

Last year I made little research to find the file formats of Monster Hunter 4 Ultimate, as with almost all capcom files, they seem to be .mca format, which has about 4 or 5 different types itself, the files of type-3 .mca can be converted to mp3 by VGMStream, and as I found VGMStream doesn't have an option to convert a .mp3 (or any other format) to a .mca beause such option is not supported.

Right now there isn't any progress about it and I think there will never be any progress.

I was thing that may be some of you who have worked with rom Hacking might help me with another little research:
is it possible for a rom hacking to replace a file with another format and be named the way the rom is supposed to read it?

I mean, if I can only have a file format readable by the 3DS (different than .mca), can I replace a .mca file in the rom with that different file format? will the rom read it?

Or may be, how could I work with the OST files of a rom to swap them with another file?

thanks for any help you can give me.