<menu>
  <item id="1"> 1111 </item>
  <item id="2"> 2222 </item>
  <item id="3"> 3333 </item>
  <item id="4"> 4444 </item>
</menu>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output method="xml" omit-xml-declaration="yes"/>

  <xsl:template match="CurrentMenuItem">
  ????
    <CurrentMenuItem>
      <xsl:apply-templates select="document('menu.xml')"/>
      <xsl:apply-templates/>
    </CurrentMenuItem>
    ????
  </xsl:template>

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

</xsl:stylesheet>

<page AppPath="" Type="Standalone">
<content> 
    <CurrentMenuItem> 0 </CurrentMenuItem> 
........
</content> 
</page>

<page AppPath="" Type="Standalone"><content> 
  ????
    <CurrentMenuItem> 0 </CurrentMenuItem> 
    ????
........
</content> 
</page>

<page AppPath="" Type="Standalone"><content> 
  ????
    <CurrentMenuItem><menu>
  <item id="1"> 1111 </item>
  <item id="2"> 2222 </item>
  <item id="3"> 3333 </item>
  <item id="4"> 4444 </item>
</menu> 0 </CurrentMenuItem> 
    ????
........
</content> 
</page>