title: Add alias/prefix to existing XML namespace
body: <p>How can I convert the following XML</p>
  
  <pre><code>&lt;root xmlns:xyz="do/not/change" xmlns="add/alias"&gt;
     &lt;name&gt;Test&lt;/name&gt;
     &lt;xyz:id&gt;100&lt;xyz:id&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>To</p>
  
  <pre><code>&lt;abc:root xmlns:xyz="do/not/change" xmlns:abc="add/alias"&gt;
     &lt;abc:name&gt;Test&lt;/abc:name&gt;
     &lt;xyz:id&gt;100&lt;xyz:id&gt;
  &lt;/abc:root&gt;
  </code></pre>
  
  <p>Using XDocument in C#</p>
  
  <p>Effectively, I want to add an alias to the second namespace, and add the prefix to all elements that do not already have a prefix.</p>
  
  <p>All the information I can find is how to remove or add a namespace, but nothing about how to add a prefix/alias.</p>