Changing the master part changes the derived parts and the assembly because they all reference the master part. In this example, you change the width of the mouse.
Tile the windows and display a Top
view of MouseMultibody.sldprt and
AssemblyMultibody.sldasm.
In the master part (MouseMultibody.sldprt), in the FeatureManager design tree, expand Sweep1, right-click Sketch1 and select Edit Sketch.
Change these dimensions:
Change 30 to 25
Change 125 to 95

Exit the sketch. Click File, Save As, and save the master part in the folder with the other multibody technique files.
The master part, MouseMultibody.sldprt, rebuilds with the changed dimensions.