title: Updating frontend layout from a module
body: <p>I've created my own magento module and successfully extending core controllers and models but I'm having trouble doing the same with the layout xml files.  I want to update just the checkout multishipping shipping page.  So far I've only managed to to overwrite the entire checkout.xml file but I would much prefer to just have the  in my xml file.</p>
  
  <p>This is what i have in my modules config.xml and the tm.xml file is in app/design/frontend/default/default/layout/</p>
  
  <pre><code>&lt;frontend&gt;
          &lt;layout&gt;
              &lt;updates&gt;
                      &lt;checkout&gt;
                           &lt;file&gt;tm.xml&lt;/file&gt;
              &lt;/checkout&gt;
          &lt;/updates&gt;
      &lt;/layout&gt;
  &lt;/frontend&gt;
  </code></pre>
  
  <p>Thanks</p>