Grading outside (invert) of a mask.

Hello,

I am trying to find a solution to an problem.

If I create a mask, how can I keep that mask and adjust the outside (inverse) of that mask, once I have made my adjustments "inside" the mask...?

See attached still: if I create my mask in red, make an adjustment, how can I then adjust the inverse space without losing what's inside the mask?

Thanks,