Thank you for the question.
I am attaching a sample project which demonstrates how you can modify the context menu in OutlookStyle. Basically, you need to take the dropdown button and then modify its menu on DropDownOpening. The tricky part is that you should do it every time a group is selected, because the button is recreated at that moment.
I hope this helps. If you have additional questions, feel free to contact me.
All the best,
the Telerik team
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