Thank ,you TiG that worked!
Any chance of incorporating the code into GlobalMaterialChange2.rbz ?
And/or a separate Plugin for displaying an option (such as "GroupCopy UnInstanting") in the Context Menu that would appear if objects are selected?
It come in handy for other issues that might happen with copied groups.
P.S.
Your previous post regarding editing a group, gave me an idea of how to make it easier to manually open multiple occurrences of groups containing materials.
I gave all groups containing materials an Instant Name that included the text "....(with material)". Then, by opening the Outliner, and searching for "(with material)" and double-clicking on each find to open and close the group. It was a fairy quick process compared to opening each group in the modeling window.
If a group's instant is properly named then all is good, BUT it takes discipline when creating groups in the first place.