I have created a stepback bookcase with some basic dimensions. I used part editor and had to save it as an assembly to get the correct faceframe placement. But now when I change the dimensions, the part editor cuts that I made get all messed up. Any suggestions as to how I can create this same stepback but be able to change the dimensions (such as height and width) so that it will all fit together correctly?
Use the Constraint Manager. Also, since you used two cabinets (one for face frames only), you will have to size that portion of the face frame separately.