Is it possible to replace audio files from one region to another in N64 games?

[esidemoken]

What's up? As the title of the post says, I would like to know if it is possible to replace the audios of a USA game with those of its Japanese counterpart.

I am referring specifically to the game Mischief Makers, I have the Japanese version and I got used to that audio and now that I am playing the USA version (to be able to understand the story xd) I find the audio of that version very strange.

So if someone knows if it is possible and tell me how to do it I will be very grateful.

[Jorpho]

Lots of things are "possible". If you are asking if it is straightforward, then probably not – especially since the N64 doesn't really have a typical "filesystem".

Music is typically ripped from N64 files as .usf files, but I'm not sure if that's applicable to sampled audio clips – though that could be a good starting point, if it is.

[FAST6191]

If you are expecting it to be as easy as a lot of CD based on DS and newer devices where there is a file system (you get either some kind of ISO editing tool or device specific ROM unpacker) and in most cases copy-paste files from one region to another with no great understanding of the underlying formats, systems or indeed audio as computers understand it then no. This is as, much as was mentioned above, the N64 has no file system and the ROMs are one giant blob.

Traditionally this then means finding the audio buried within the relevant regions and copying things across before redoing pointers and whatever else. This is actually quite hard for many people so it is often more preferable to backport the game's script instead to the region of your choice.
Issues with things here can happen if the game's audio quality is lowered or improved, audio is lost (N64 era voice acting might have been expected in Japan but nobody really cared outside it, indeed still happens to this day. Worse is when quality is crushed to fit on a smaller cartridge or something as that poses greater artistic questions) which in turn means most of the calls to it will have to be recreated (the N64 being a compiled console means things are rarely just blanked out at code level and might no longer exist), extra audio being created (more of a thing for remasters and later version ports but can happen between regions, and can also be more of a thing with multi language European versions).

In more recent times it seems theoretical computing collided with the real world and decompilation of a program became viable such that you end up with source code you can compile (Mario 64, Zelda Ocarina of Time and Perfect Dark being the big three so far, Kirby is coming along I believe and there are a few more). If then your game has been decompiled the ease with which things can be changed increases dramatically (maybe not quite to the file system thing seen elsewhere but not so very far removed, and you can add more things). if you are asking this sort of question you are not going to be making a decompilation any time soon yourself. I have not seen anything on this game being taken on but at the same time decompilation is a legally dubious concept so it does often happen in private, and I can see this being one of the bigger remaining high profile targets.
From legally dubious to unquestionably legally troublesome is leaked code, of which there has been a bit now (see gigaleak). Nintendo did publish it in some regions but I don't think it was part of the leaks.