10.06.2015-node_teasers-hook_entity_view_mode_alter.php

<?php

/**
 * Implements hook_entity_view_mode_alter().
 */
function midd_entity_view_mode_alter(&$view_mode, $context) {
  if ($context['entity_type'] == 'node' &&
      $context['entity']->nid != arg(1) &&
      $context['entity']->type == 'news') {
    $view_mode = 'teaser';
  }
}