Replacing values in XML is easy with XmlTask

http://www.oopsconsultancy.com/software/xmltask/

especially the replace command is quite useful:

  <xmltask source="../${env.BUILD_ENVIRONMENT}/tmp/System/SMTP_Servers/EmailServer.SMTPServer" dest="../${env.BUILD_ENVIRONMENT}/tmp/System/SMTP_Servers/EmailServer.SMTPServer">
    <!-- change email server URL -->
    <replace path="/xml-fragment/*[local-name(.)='serverURL']/text()" withText="${EmailServer.smtp.Server_URL}"/>
    <!-- change email server port number -->
    <replace path="/xml-fragment/*[local-name(.)='portNumber']/text()" withText="${EmailServer.smtp.Port_Number}"/>
  </xmltask>
  

as explained in this excellent post, you can use it to customize a OSB project