If I understand you right and you use the java node structure for matlab than you could use this function to replace the node:
%Function to replace a w3c node
function xmlreplacenode(node1,nodenew)
parent = node1.getParentNode;
node1.getParentNode.removeChild(xmlnode);%Delete the node
parent.appendChild(nodenew);
If not you should first parse the document with:
xDoc = xmlread(handles.tmpverzeichn);
You still need a function to generate a new node from a string maybe. For that you can try this:
%input doc is java org.w3c.dom Document
%str is a xml string
function node = parsestr2node(doc,str)
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
import org.w3c.dom.Node;
import java.io.*;
inStream = org.xml.sax.InputSource();
inStream.setCharacterStream(java.io.StringReader(str));
docBuilderFactory = DocumentBuilderFactory.newInstance();
docBuilder = docBuilderFactory.newDocumentBuilder();
tmpdoc = docBuilder.parse (inStream);
node = doc.importNode(tmpdoc.getChildNodes.item(0),true);
If it doesn t work maybe you need some java files
