In drupal 7, I'd like to be able to change the page template if a value is returned in a CKK field. 

I tried: 

function themename_preprocess_page(&$variables) {

      $node =  $variables['node'];

      if($node->type == 'page') {

           if (isset($node->field_change_theme['und']['0']['value'])) {

                   $variables['theme_hook_suggestions'][] =  'page__newtheme.tpl.php';

          }

     }

}

A value is being returned but the theme is not changed.   Please help.

Thanks,
Tracey