How to "trim" bodies in an assembly in Solidworks?
I don't think there is anything that easy in the assembly level but here are 2 different ways I would do it instead of opening every part and finding the sketch etc...
Right click the part you want to change and click "Edit Part"
This will let you edit the part while you are in the assembly.. (Makes everything else transparent)
Select a suitable face, and create a sketch on it
Select "Convert Entities" from the ribbon or Tools>Sketch Tools from the menu bar. Then Select the inner diameter of the green Cylinder, and click the green check.
It will project that circle to your selected face in that part, click OK.
Do an extruded cut and select the region between your newly created circle and the purple cylinders outer diameter. Select "Through All" instead of "Blind" and accept.
Return to your assembly and the purple cylinders O.D. now matches the green cylinders I.D.
Right click the feature you want to change and click "Edit Sketch"
Alter the value to the desired size. (1.625 to 1.500 in this case)
Click OK, exit the sketch and return to the assembly.
Hope this helps!