Perhaps I am missing something in the UI, but I do not see a way to change a mask after creating it. To clarify, I do see the Adjust Mask entry, and that allows me to expand or contract the mask, to feather it and make contrast and density changes. What I do not see is any way to erase part of the mask if I have over-painted it.
For example, I was masking a bird with the Edge Aware set to ON, but the mask still picked up part of the sky. I wanted to erase that small part, but could find no way to do that. I did see that I could invert the mask and add to the new mask (thus I suppose erasing part of the original mask), but is that the only way to correct over-painting? Or am I just missing something?