To begin with, where is the mass of a black hole? If we are not able to define a location in spacetime for that mass, we could think just about the deformation of spacetime around the event horizon.
How does Hawking radiation reduce the energy and mass of the black hole? Talking about particle pairs, does the negative energy particles annihilate with the particles inside the event horizon and if so, could that interaction which occurs inside the event horizon affect the event horizon radius?