Custom Shading Model, Lambert with Blinn-Phong

Is there any official documentation about how to implement a custom shading model in UE5.6?

I can’t seem to find anything at all and most other tutorials in the internet all years old. Is there an up-to-date video or written guide somewhere?

If not, could someone point me to all the files I need to edit in 5.6 so I can declare a new shading model and use it in the material editor? That would really help me out, because the default GGX isn’t distinguishable enough from other games imo. I’d like to make my project really stand out.

Thank you