Where to look for customizing mesh import?

I want to customize importing process of some meshes. Specifically, I want to change how materials are created and type of the material - I need one unlit material with many instances instead of many lit materials (which are created by default when I import the mesh).

Where to look for such thing in the engine source code?

I’m using OBJ file format by the way.

Ended up creating custom UFactory from scratch.