Thanks Jamsh!
Just to clarify, would I need to use the VS 2015 Community compiler to build the UE4 source code? I’ve never done something like work with source code before - at least, not yet 
If, say, I figure out a unique way to make UE4 work with BRDFs effectively do I just upload the source code to the GitHub panel so that it gets integrated into further revisions of the engine?