When I click the 'Dup' button on the 'Configure Statistics' dialog either for a protected Column or Statistic, a new item is created and I am able to edit the Name, but can't change anything else or click Save, etc. until I select another item in the Existing Column/Statistic list. Then it asks if I want to save, say yes, then I can choose the new duplicate item and edit it properly.
Related request: It would be useful to be able to highlight and copy text from protected items, even though we can't edit them, if we want to use something similar in a custom item.