Adding custom post processing?

[FiftyTifty]

Been taking a look at Community Shaders with the Vanilla HDR shader, and I'd like to try adding a few simple post processing effects. What's the best way to go about this?

I've ported (simple, not things like bloom or AO) HLSL code between ReShade & ENB & NVR, so I got that side of things covered. But how do we add our own in before the game gets clipped to SDR?

A quick glance and it looks like I'd have to make direct edits to Vanilla HDR's code, and no way to insert our own without conflicting?