How do I do a deep copy of an element in LINQ to XML?

There is no need to reparse. One of the constructors of XElement takes another XElement and makes a deep copy of it:

XElement original = new XElement("original");
XElement deepCopy = new XElement(original);

Here are a couple of unit tests to demonstrate:

[TestMethod]
public void XElementShallowCopyShouldOnlyCopyReference()
{
    XElement original = new XElement("original");
    XElement shallowCopy = original;
    shallowCopy.Name = "copy";
    Assert.AreEqual("copy", original.Name);
}

[TestMethod]
public void ShouldGetXElementDeepCopyUsingConstructorArgument()
{
    XElement original = new XElement("original");
    XElement deepCopy = new XElement(original);
    deepCopy.Name = "copy";
    Assert.AreEqual("original", original.Name);
    Assert.AreEqual("copy", deepCopy.Name);
}