Deferred Shading uses in Unreal

Hi All,
I was using UE4 for one of my research project on shader development and I need to use custom deferred shader for it. I was looking for a way to use shader options inside UE4 but I didn’t found one. I look up into the Unreal source code but I was unable to find the entry point of the shader selection during runtime. Could anyone help in this regard?