Illustrator :: How To Resize Shape(s) That Has Been Drawn Using 3D Guides

I've created a very basic shape using the 3D grid as my guide - picture if you will 4 boxes, one on top of each other (as per illustration below):
 
Each "box" is made up of 3 shapes to give the 3D effect.
 
I need to resize one of the boxes, the yellow one, which needs to be resized in keeping with the 3D framework (making it smaller in height), and then placing the yellow box above the purple box. How this can be done without having to redraw the shapes in the required positions.
 
I might add it is the grouped shapes that makes up the box which I am trying to resize in one hit, as opposed to the individual shapes.