Make a custom view mode default
This is the way i set the 'fullpage' view_mode of a node as default:

&lt;?php
/**
 * Implements hook_entity_view_mode_alter().
 */
function YOUR_MODULE_entity_view_mode_alter(&amp;$view_mode, $context) {
  // Set default view mode.
  if (isset($context['entity']-&gt;nid)) {
    if ($context['entity_type'] == 'node' &amp;&amp; $context['entity']-&gt;type == 'YOUR_CTYPE' &amp;&amp; $view_mode == 'full') {
      $view_mode = 'fullpage';
    }
  }
}


It actually sets the view_mode to 'fullpage' when in full mode (default), but you could ommit that part (&amp;&amp; $view_mode == 'full').

Remember that 'fullpage' is the machine name of my view_mode and 'YOUR_CTYPE' is the machine name of your content type.

Not sure if this will work with Display suite though...