This mod aims only at adding music disc customization into 1.12.2 and nothing more.
Enjoy the music.
A simple tutorial and example can be found on Github at Source page.
Version 1.1 added the json generation and a fix, check it out on Github for more detailed information.
Notice: this mod has nothing to do with anything else, like adding a custom recipe for discs (As CraftTweaker can do much better than me), so you may use it along with other recipe-editing mod to get in in survival.
Version 1.2
VERY IMPORTANT: Due to a really stupid mistake, I forgot to make a server side check and any version before 1.2 will absolutely break when running on a dedicated server. This is fixed in 1.2 now.