How to change label text of built-in tab dynamically in MS Excel

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C#

Office-Automation

Hi
I need to change the name of the Insert tab dynamically using C# addin. I am using MS Office 2007. I tried the following xml, I can see my custom group and button in insert tab but tab name is not getting changed.

<?xml version="1.0" encoding="utf-8"?>
<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui" >
  <ribbon>
    <tabs>
      <tab idMso="TabInsert" getLabel="GetLabelText">
        <group id="CustomGroup" label="MyGroup" insertAfterMso="GroupInsertTables">
          <button id="Open" getLabel="GetLabelText" onAction="OnOpenClick"/>          
        </group >
      </tab>
    </tabs>    
  </ribbon>
</customUI>

GetLabelText function for button is getting called but for tab it is not. If I use label="MyInsert" attribute it is working but getLabel attribute is not working for built-in tabs. Is this property not supported for built-in tabs ? or Am I missing something?