You can't decompile MCCC, it's done that way on purpose because people were stealing from him. You could try to find a really old version before he implemented this change, but it's been several years and the code will be outdated in some parts. I would recommend looking at other mods instead and if you have questions, join the Creator Musings server linked in my signature. There's modders and resources there to help with your questions (there are no scripters who frequent these forums enough to catch any possible questions).
Creator Musings is a Sims 4 modder, poser/animator, and CC creator hangout server (though everyone is allowed) with a tutorial/resource directory, help channels, and mod/cc/sims 4 news channels! My Discord | Twitter | Tumblr | Patreon