I am interested in creating a custom colour management profile. How you can get an image that looks very different depending if you use log or film or false colour, except I want to try and create a toon profile. One that will basically take the millions of colours normally rendered and round them to the nearest colour available of say a couple hundred.

Yes I know this is possible through shaders, but this requires manual tweaking of every material for every scene and every light. For a small project sure, but not for a large project with many scenes. There has to be a way for blender to do this in a "smarter" way.