Applying Player-Made Custom Models on Android

While there are some add-ons that allow model changes to models created by add-on authors (separate from the so-called 4D skins intended for iOS), there's not much information available on how to create add-ons for changing to custom-made models. I'd like to try it, but it seems like it'll be quite difficult... In the first place, my custom model itself is still unfinished.