Yes, you should be able to merge the code and keep up to date. I can’t promise that would be trivial, but we’ve been doing for years with UE3 and Perforce. I think the Github system should make it much easier. Of course, if your customized branch makes fundamental changes to the renderer or other systems that are touched by WaveWorks, VXGI, FleX, etc., you will have more work to do when you merge.