Hacking Any ways to inject audio into the 3DS sounds (sound effects) app?

[cerealandchoccymilk]

I use Flipnote 3D for little animation projects, which requires the use of the sounds app, specifically the 10-second sound effect speech bubbles. It would be so much easier if I could just inject my existing sound file into it so I have more control over volume, recording quality, start timing, etc.
I did try trimming my audio to under 10sec, converting to m4a, and replacing an existing sound effect with that on the SD card, but it just ended up greyed-out and unplayable.

I understand if this is straight up impossible but it would be nice if there's a way
This is an O3DSXL with the latest Luma and Homebrew.

 

[ultradens]

does this help?

 

[deckerboii]

does this help?

I think that's for Nintendo 3DS Sound only, but I don't know since I don't play Flipnote 3D