This quick tutorial is related to my fellow students at (amazing) Animation Mentor who have their given rigs and want to scale or mirror them.
Since it´s not recommended to change the rigs and scaling in general is a dangerous thing in animation you can do a little bypass for small changes (like scaling a ball or Tailor, etc.)
align it to the given master control
and make the new shape the parent of the ball’s master control.
You should name this! For example „Scale CTRL“. This works for mirroring (negative scaling), too!
In addition to that you can simply choose the mirror axis by rotating the „Scale CTRL“ the way you want BEFORE parenting the master control to it. Or unparent it temporarily.