Can you be more specific about what you mean by the compositing mode? What old options were there? Also, what would you like it to do?
I see. I currently cheat those by doing a couple things. Additive mode is achieved by turning off lights, setting Color and Absorption to 0 and Emission to non-zero. I do data passes like z-depth or normals by turning off lights, setting the data to the Emission channel, Absorption to full white and density REALLY high. But I see your point, this could be easier and it certainly doesn’t allow crazy custom stuff.