Texture luminosity mask (apply texture to shadows)

I wanted to recreate this look from Serial Experiments Lain just for fun in a game (blood spots in the shadows). I guess the best way to do it is to use a mask to apply a blood texture just to a certain range like 0-50, with proper fading of course. I don't know how to code shaders, so I'd really appreciate if someone could give it a try.

Hello,

Since Lain was a favortie of mine, i gave your idea a try :
Go there : github.com/AlucardDH/dh-reshade-shaders
You need DH_Lain.fx and the 2 textures : lain_blood_1024.png and lain_cloud_1024.png

The blood texture could be better but you can change it
There is also a few parameters to customize the rendering to your liking.

Thank you so much!