You just have to decompile the game, I use godmode 9 to do that, all the games and some of their files come in a folder called "romfs" whenever you are going to make a modification to the textures or music, you create a folder in luma/ titles and the id of the title and put inside a folder...
English:
Hello!
I'm here to publish this mod I made for the 3DS version of Terraria, which consists of changing all the music in the game for Undertale music! I hope more than one likes it
Don't forget to visit my page and see more mods like this!
Sorry, look for my profile on Github "mizakko"...
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi