ROM Hack How to ROM Hack 3DS?

[Chara-Ann]

I am not sure where to look and have not found any tutorial over the subject and was wondering exactly how to ROM hack? In the game AC:NL specifically, I have looked at the creation of custom textures for villagers, trees, etc., custom dialogues, and the lot. I also was wondering how to replace the music in the AC:NL game with custom music. I saw something that appeared to be working with extracted ROMfs. I have no clue what ROM is, how to access it, or how to work with it. I do not remember what I did, but in the past I attempted to create my own textures and map tiles/layers or however for the PC game Stardew Valley. I did something with the files and got access to the images of all the tiles/furniture/trees/objects/etc. I also did some sort of code stuff. Does not help much probably since I don't retain any knowledge of it. Where do I start? How do I find the AC:NL game files and what do I do with them to access them so I can edit them to create custom textures or replace the music? For the music, I know how to convert mp3 to .bcstm from trying to create custom 3ds themes though I am not sure what settings to apply when editing AC:NL sound files such as the looping, the mono something, and the Hz. I have no idea what I've just said, but some dumbed down step-by-step help would be appreciated. I know no one may have the time to get really in-depth with the topic to best help me. Honestly really, big thanks to anyone who has taken the time to read this or deal with the matter.

Edit: I believe I may have gained access to the romfs and am currently attempting to edit the textures, etc. I have forgotten how I did this unfortunately , but hopefully I will be able to edit them and reinsert everything back into the correct places and make it work. Let's see!