P: (Masking) Use previous masks as objects for add/subtract

Woudl love to be able to select a previous mask when adding/removing. For example, I shoot a lot of lifestyle/product images on a Fjord in Alaska like the ones attached. I mask the beach, water, mountains and sky separately.

When masking the mountains, it would be great so select background, subtract sky, then subtract pre-existent mask "Ground" and mask "Water" that I have already created. That would ensure a perfect boundary between the two and make the flow really quick.