Best composite/overlay mode for affecting only highlights.

What is the best composite mode to use if my goal is to apply noise only to my brightest highlights?

I commonly find that while I may want to denoise the shadows and midtones of my image, I kind of like the aesthetic of grainy/noisey highlights.

I have some film grain overlays that I'd like to affect only my highlights, perhaps rolling off gently as image goes toward midtones.

Maybe some kind of gradient denoiser?

Any ideas?