<WindowBuilderProject>
  <stringtable>

    <stentry>0..607</stentry> //All of the other records

    <stentry>
      <index>608</index>
      <sid>MNUB_AUTO</sid>
      <val>
        <en>AUTO</en>
      </val>
      <params>
        <fontref>0</fontref>
        <numref>0</numref>
        <clip>FALSE</clip>
        <include>TRUE</include>
        <protected>FALSE</protected>
        <cwidth>-1</cwidth>
        <dwidth>0</dwidth>
      </params>
    </stentry>

  </stringtable>
</WindowBuilderProject>

string location = "/WindowBuilderProject/stringtable/stentry[index='" + rowIndexOfItemUnderMouseToDrop + "']";
XmlNode Copy = xDoc.ImportNode(xDoc2.SelectSingleNode(location), false);
xDoc.DocumentElement.AppendChild(Copy); //This is just supposed to add it to the end, I will worry about ordering once it works

var xDoc1 = XDocument.Load("C:\text1.xml");
  var xDoc2 = XDocument.Load("C:\text2.xml");

  var doc1Entries = xDoc1.Descendants("stentry");

  var cloneEntries = doc1Entries.Select(x => new XElement(x));
  xDoc2.Descendants("stentry").Last().AddAfterSelf(cloneEntries);

  xDoc2.Save("C:\text2.xml");

var filterIndices = new[] {600, 601, 700, 705};

  var doc1Entries =
      xDoc1.Descendants("stentry")
           .Where(x =>
               filterIndices.Contains(int.Parse(x.Element("index").Value)));