Masking addition/subtraction simplification

I'd made this suggestion a bit ago and was told that brushes do reverse via the option key. Partly true. Mostly not. So I'll try to be more specific here.

If I use AI to subject mask (generally very good) but it missed some part of the subject I must go to the drop down menu and select "add to mask > brush" and then I can paint in on the AI mask what was missed. BUT! the option key will only allow me to subtract what I just painted with the brush - it will not allow me to subtract from the original AI mask. To subtract from that mask I need to go back up to the menu and select "subtract from mask > brush" so I think my original point stands. Adding and subtracting are not seamless and intuitive.

Also, within a mask there is no way to key command between brushes. B is simply brush and E is simply erase. I'd like to be in a mask and chose between magic brush or regular brush and then use the option key to reverse within the original (let's just say) AI mask.