Does anyone know how to add a new ncg.bin file? It is so I can change one of the duplicate tileset options without changing the others, and if I use the ncg.bin (The tileset is the "Bonus room (unused)") file and then save it, it will affect the others that use the same tileset because they all use the same ncg.bin file, so I am hoping to counteract that by just adding a new ncg.bin file, but I can't figure out how to do that.

To my knowledge, you can't get a tileset slot to load different graphics and collision n such without ASM. If you need more tilesets, you can probably use MeroMero's dedicated tilesets per area patch.