I’m kinda sad after moving from unity (where I’ve done a shitload of custom lighting).
Who knew that unreal did not give us ability to customize lighting response in the editor (even if it would be HLSL/GLSL/whateverSL)
What I did here is adjust world space normals to get more or less a cell-shaded look. It kinda messes up with normal edge detection and is not really accurate… Final color / baseColor doesn’t work properly also. It looks like there is no other way than to adjust the engine code 
This is the closest I’ve got to my style:
This is what I have in Unity, which I’m trying to repeat here:
