title: Magento - Add node and save module config
body: <p>I try to add a node to the module config like this:</p>
  
  <pre><code>$model = Mage::getConfig()-&gt;getModuleConfig('lemike_devmode');
  $model-&gt;setNode('foo/bar/baz', 'qux', true /* overwrite */);
  var_dump($model); // empty Mage_Core_Model_Config_Element
  </code></pre>
  
  <p>But it does not create the new nodes. The <code>$model</code> is just empty.</p>
  
  <p>What went wrong here? </p>
  
  <p>After that I guess <code>Mage::getConfig()-&gt;saveCached()</code> is correct for saving the new node, or?</p>