Only thing that comes to mind would be to run a PowerShell script post export that would do the renaming for you, you can can call the script from the QlikView script using CMD.exe /c etc. That is about the only means of which I see to do this. The only other thing would be to submit an idea in Community to allow renaming, but it did just occur to me that you should be getting dialog to do this:
You appear to have left out some details that are pertinent, please leave further clarification, but I would recommend reviewing Help content on what you are trying to do in order to be sure you are seeing expected behavior according to the documentation.
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