Something I made a few days ago, a "port" from Fire Emblem: Three Houses. As it is, it will go over "Id (Purpose)" (SSBU Remix), but you can change it so that it will go over a different song. If you do want it over a different song (in the FE series) it will have to be one of the following;
Edge of Adversity - bgm_j30_ssk_shituinohate.nus3audio
Fire Emblem Theme - bgm_j02_fem_theme.nus3audio
The Apex of the World - bgm_j48_fsg_konosekainoitadakide.nus3audio
Id (Purpose) [SSBU Remix] - bgm_j39_ksi_i_i.nus3audio -------- (This is where is will go as it is)
The Edge of Dawn (Seasons of Warfare) (JP) - bgm_j43a_fsg_hraesvelgrnoshoujo_fuukasetsugetsu.nus3audio
The Edge of Dawn (Seasons of Warfare) - bgm_j43b_fsg_theedgeofdawn_seasonsofwarfare.nus3audio
All you have to do is rename the ".nus3audio" file to the file name that corresponds to the song you want from above from the list above. If you want to put it over a song not from FE then you will have to go to SmashUlimateTools and find a song that is LARGER than the .nus3audio file that I gave you (down to the byte), the song (when in .nus3audio) you want replace has to be larger than the song (when in .nus3audio) you are replacing it with. From there you can either just put a random mp3 (or wav or any other supported format) so you can get the file name that your vanilla song is under, or you can join the SSBU Modding server and use the bot there (#conversion-bot) to get the vanilla file name from the bot.
I will probably be posting a another "Mod" for the "Rain" version of the song.