about film grain in layer mask Merged

I have an interesting question from one of my audiences, which is about film grain with layer function. Far as we know, film grain is effect the whole picture, but this audience told me that one of his photos need to use two different type of grain in single image (fine grain for highlight area or people area and silver in shadow), however this is not working with using layer mask. as now CO has layers for skin, color edit, is that possible that film grain can also work with layers?