In case that you want to allow the users to add the same Content as the current one in the tab is by defining the content in different UserControl (just like you mentioned) and adding another copy when the user request it. This is the cleanest and safest way.
Another possible approach would be to try and create a DeepCopy of the elements that you want to copy, please take in mind that this approach might not work in all cases.
I hope this information helps. Please let us know if you need further assistance.
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