Most efficient way to overlay effects.

[LilyMakesThings]

A lot of my friends want a post-processing extension for TurboWarp that can render effects like blur and tints onto the project window, like this.

I want to create such an extension, but I'm unsure as the best way to go about doing this. Assuming it would be possible, what's the most efficient way of altering what is rendered through a project to add effects like this?