After I duplicate linked ( Alt-D ) a group of objects can I unlink one of the object to do editing work on it? So it will not affect the rest of the object?
Yes, U in Object mode and choose.
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For mesh-objects you can also click (Make it a single user) on the number button (it displays how many object use this mesh) between the ME: field and the F button in the Links and Materials Panel (Editing [F9] context).
This works exactly the same for lamps (it’s called LA: here instead of ME:) etc…
Werner
thanks everyone - I needed 3 of the same object in different colors - awesome tips and workflow ideas.