You need to take cloned element and add it to the node where you need it to be. It can be your root node, your outer OI node or another XML document. But you have to have node.Add (clonedNode) somewhere.
Also, consider using XPath to select OI node precisely, this LastChild.LastChild.LastChild creates structural dependancy and your code will break if someone adds even <br /> at the end of your XML.
Instead, select
rootNode.SelectSingleNode("//ExportedObjects");
and work from there.