How to add DOCTYPE to xml file using xmlport in Version 2009

fnk_doIt(par_re_Item : Record Item)

// Create file
fi_XMLFile.CREATE(te_XMLFilePath + te_XMLFileName);

// Create OutStream
re_TempBlob.Blob.CREATEOUTSTREAM(os_OutStream);

// Run XML-Port and write in OutStream
xp_Item.SETTABLEVIEW(par_re_Item);
xp_Item.SETDESTINATION(os_OutStream);
xp_Item.EXPORT;

// Load it into a Blob
re_TempBlob.Blob.CREATEINSTREAM(is_InStream);

// TODO: look for the first representation of a linebreak(or something else), instead of reading a hardcoded number of chars
// Read and write line 1
IN_NumberOfChars := 56;   // Number of chars from line 1
FOR i:=1 TO IN_NumberOfChars*2 DO BEGIN   // *2 because XML-Port generates 4 byte blocks and a Char has 2 bytes
  is_InStream.READ(CH_char);
  fi_XMLFile.WRITE(CH_char);
END;

// Make a line break
// Xml-port makes a line break like this: 0D 00 0A 00 (Hexadezimal)
// The write function writes minimal 4 bytes, so you can't write those chars(0D,0A,00) one by one
// 655373 stands for 00 0A 00 0D; it starts writing with the last byte
fi_XMLFile.WRITE(655373);

// Make your extra line
TE_InsertText := '<!DOCTYPE Transaction PUBLIC BlaBlaBla';
FOR i:=1 TO STRLEN(TE_InsertText) DO BEGIN
  fi_XMLFile.WRITE(FORMAT(TE_InsertText[i]));
END;

// Read and write rest
WHILE NOT is_InStream.EOS DO BEGIN
  is_InStream.READ(CH_char);
  fi_XMLFile.WRITE(CH_char);
END;

// Close file
fi_XMLFile.CLOSE;

Name	DataType	Subtype	Length
re_TempBlob	Record	TempBlob	
xp_Item	XMLport	Item	
te_InsertText	Text		1024
te_XMLFileName	Text		30
te_XMLFilePath	Text		900
ch_char	Char		
i	Integer		
in_NumberOfChars	Integer		
fi_XMLFile	File		
is_InStream	InStream		
os_OutStream	OutStream			

MSDOM.loadXML('<?xml version="1.0" encoding="utf-8" standalone="no" ?>' + Separator
      + '<!DOCTYPE cXML SYSTEM "http://xml.cXML.org/schemas/cXML/1.2.009/InvoiceDetail.dtd">' + Separator + '<ROOT></ROOT>');
<ROOT></ROOT>

    VAR
      XMLDOMDocument : Automation :'Microsoft XML, v6.0'.DOMDocument;
      OutboundInvoice : Record 112;
      TempBlob : Record 99008535;
      TempOutstream : OutStream;
      TempInstream : InStream;
      OutboundInvoiceXML : XMLport 50001;
      MSDOM : Automation :'Microsoft XML, v6.0'.DOMDocument;
      XMLNode : Automation :'Microsoft XML, v6.0'.IXMLDOMNode;
      XMLNode2 : Automation :'Microsoft XML, v6.0'.IXMLDOMNode;
      Separator : Text[30];
      Ch10 : Char;
      Ch13 : Char;
      Ch9 : Char;

    PROCEDURE AddDocType();

      IF ISCLEAR(XMLDOMDocument) THEN BEGIN
        CREATE(XMLDOMDocument);
        XMLDOMDocument.async := FALSE;
      END;

      OutboundInvoice.SETCURRENTKEY("Sell-to Customer No.","External Document No.");
      OutboundInvoice.SETRANGE(OutboundInvoice."No.",'PI103815');
      IF NOT OutboundInvoice.FIND('-') THEN
        ERROR('No Invoice Found');

      TempBlob.Blob.CREATEOUTSTREAM(TempOutstream);

      OutboundInvoice.SETRANGE(OutboundInvoice."No.",'PI103815');
      OutboundInvoiceXML.SETTABLEVIEW(OutboundInvoice);
      OutboundInvoiceXML.SETDESTINATION(TempOutstream);

      IF OutboundInvoiceXML.EXPORT THEN BEGIN
        TempBlob.Blob.CREATEINSTREAM(TempInstream);
        XMLDOMDocument.load(TempInstream);
        ChangeXMLFile(XMLDOMDocument);
        XMLDOMDocument.save('C:\xmlfilewithDocType.xml');
        MESSAGE('Xml Export completed! C:\xmlfilewithDocType.xml Created');
      END ELSE
        ERROR('Error exporting');


    PROCEDURE ChangeXMLFile(VAR MSDOM2 : Automation :'Microsoft XML, v6.0'.DOMDocument);

      IF ISCLEAR(MSDOM) THEN BEGIN
        CREATE(MSDOM);
        MSDOM.async := FALSE;
      END;

      Ch10 := 10;
      Ch13 := 13;
      Ch9 := 9;
      Separator := FORMAT(Ch13) + FORMAT(Ch10) + FORMAT(Ch9);

      //Cancel validation because loadXML will try to send to parser and it will fail because of external DTD
      MSDOM.validateOnParse(FALSE);

      //Insert the header you want/need to use.  It seems you must have root or something like it.
      //You can add a boolean in front of this command to verify that it loaded.
      MSDOM.loadXML('<!DOCTYPE cXML SYSTEM "http://xml.cXML.org/schemas/cXML/1.2.009/InvoiceDetail.dtd">' + Separator
        + '<root></root>');

      //If you need to replace the <root> with your first element use this.
      //My first element I wanted to keep was called <cXML>.
      XMLNode := MSDOM.selectSingleNode('root');
      XMLNode2 := MSDOM2.selectSingleNode('cXML');
      MSDOM.replaceChild(XMLNode2,XMLNode);

      //If you wanted to keep the <root> use this instead.
      //XMLNode2 := MSDOM2.selectSingleNode('cXML');
      //XMLNode := XMLNode2.cloneNode(TRUE);
      //MSDOM.documentElement.appendChild(XMLNode);

      //These were made for testing...
      //MSDOM.save('C:\Test1.xml');
      //MSDOM2.save('C:\Test2.xml');

      MSDOM2 := MSDOM;