Rename/Replace Node name with prefix

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XML

Hi. I need to add the prefix user to the bold nodes.
I tried to manipulated as string. but i always get the namespace error.

Can some1 some one please guide me. Thnx thanks

<?xml version="1.0" encoding="utf-8"?>
<user:enterprise xmlns:user="http://www.imsglobal.org" >
  <webserviceheader>
    <commitfrequency>1</commitfrequency>
    <checkexternalidfirst>N</checkexternalidfirst>
  </webserviceheader>
   <person>
    <UserId>2</UserId>
    <Name>
      <FN>Sammy Sam</FN>
    </Name>
    <Email>Sam@yahoo.com</Email>
    <Adr>
      <address1>Vacoas</address1>
      <address2>Phoenix</address2>
      <country>Mau</country>
    
    <Extension>
      <Password>LOL2</Password>
      <Manager>Boss1</Manager>
    <Extension>
</person>
    <UserId>3</UserId>
    <Name>
      <FN>Johson Thomas</FN>
    </Name>
    <Email>Tom@yahoo.com</Email>
    <Adr>
      <address1>Pereybere</address1>
      <address2 />
      <country>Mau</country>
    </Adr>
<b>    <Extension>
      <Password>LOL3</Password>
      <Manager>Boss3</Manager>
    </Extension>
  </person></b>
</user:enterprise>

[Edit: added code tags]