Ultimate Music Replacement Mod
A Skyline plugin for replacing stream files (music, movies) with files of arbitrary size.
Mod files go in the following location:
/atmosphere/contents/01006A800016E000/romfs/stream/
For example, you can replace the menu music by placing a .nus3audio file here:
/atmosphere/contents/01006A800016E000/romfs/stream/sound/bgm/bgm_crs2_01_menu.nus3audio