What I usually do, copy the mask change the size of the solid, and paste it again. A circular mask will remain circular, and not turn into an elipse, like if you would have resized the old solid..
It’s ok if you only have a few layers, but if you have lots.. it’s no the best.
Alternatively, you could use the old solid as a track matte for the new solid.
maybe there’s even a script out there to do this..?