PowerShell XML - gleichen Child bei allen Nodes hinzufügen

function Transform-XML {
    param(
        [string]$stylesheet,[string]$xml
    )
    try{
        $xslt = New-Object system.xml.xsl.xslcompiledtransform
        $xsltstream = New-Object System.IO.MemoryStream
        $xmlstream = New-Object System.IO.MemoryStream
        $outputstream = New-Object System.IO.MemoryStream
        $xsltbuffer = [System.Text.Encoding]::UTF8.GetBytes($stylesheet)
        $xmlbuffer = [System.Text.Encoding]::UTF8.GetBytes($xml)

        $xsltstream.Write($xsltbuffer,0,$xsltbuffer.length)
        $xmlstream.Write($xmlbuffer,0,$xmlbuffer.length)
        $xsltstream.Position = 0
        $xmlstream.Position = 0

        $xsltreader = [System.Xml.XmlReader]::Create($xsltstream)
        $xmlreader = [System.Xml.XmlReader]::Create($xmlstream)
        $xslt.Load($xsltreader)
        $args = [System.Xml.Xsl.XsltArgumentList]::new()
        $xslt.Transform($xmlreader,$args,$outputstream)
        $outputstream.Position = 0
        $result = [System.IO.StreamReader]::new($outputstream).ReadToEnd()
        $xsltstream.Dispose()
        $xmlstream.Dispose()
        $xsltreader.Dispose()
        $xmlreader.Dispose()
        $outputstream.Dispose()
        return $result
    }catch{
        write-error $_.Exception
    }
}

$myxml = @'  
<?xml version="1.0" encoding="UTF-8"?>  
<PRODUCTS>
     <SPAREPARTS>
          <FATHER>02X_HBZ310</FATHER>
          <PART>02X_HBZ103</PART>
     </SPAREPARTS>
     <SPAREPARTS>
          <FATHER>02X_HBZ310</FATHER>
          <PART>13X_EFLB1303S2</PART>
     </SPAREPARTS>
</PRODUCTS>
'@  

$mystylesheet = @'  
<?xml version="1.0" encoding="UTF-8"?>  
<xsl:stylesheet version="1.0"  
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">  
<xsl:output method="xml" indent="yes"/>  
<xsl:strip-space elements="*"/>  
<xsl:template match="@*|node()">  
    <xsl:copy>
        <xsl:apply-templates select="@*|node()"/>  
    </xsl:copy>
</xsl:template>
<xsl:template match="/PRODUCTS/SPAREPARTS">  
    <xsl:copy>
        <xsl:apply-templates select="@*|node()"/>  
        <GROUP>XGROUP</GROUP>
    </xsl:copy>
</xsl:template>
</xsl:stylesheet>
'@  

Transform-XML -stylesheet $mystylesheet -xml $myxml

<?xml version="1.0" encoding="utf-8"?>
<PRODUCTS>
  <SPAREPARTS>
    <FATHER>02X_HBZ310</FATHER>
    <PART>02X_HBZ103</PART>
    <GROUP>XGROUP</GROUP>
  </SPAREPARTS>
  <SPAREPARTS>
    <FATHER>02X_HBZ310</FATHER>
    <PART>13X_EFLB1303S2</PART>
    <GROUP>XGROUP</GROUP>
  </SPAREPARTS>
</PRODUCTS>

function Transform-XML{
    param(
        [string]$xsltfile,[string]$xmlfile,[string]$xmlfileout
    )
    try{
        $xslt = New-Object system.xml.xsl.xslcompiledtransform
        $xslt.Load($xsltfile)
        $xslt.Transform($xmlfile,$xmlfileout)
    }catch{
        throw $_.Exception.Message
    }
}

Transform-XML -xsltfile 'D:\transform.xslt' -xmlfile 'D:\test.xml' -xmlfileout 'D:\test_new.xml'