Allow raw meta tags to be modified prior to rendering (D7)

To alter a meta tag in hook_metatag_metatags_view_alter() is pretty cumbersome as I have to mess with the render array:

function MY_MODULE_metatag_metatags_view_alter(&$output, $instance, $options) {
  $output['title']['#attached']['drupal_add_html_head'][0][0]['#value'] = 'My fancy title';

  // Changing a page from "index" to "noindex" requires string manipulation...
  $robots = &$output['robots']['#attached']['drupal_add_html_head'][0][0]['#value'];
  $robots = str_replace(' index', ' noindex', $robots);
}

There should be a hook_metatag_metatags_alter() to allow altering the meta tags before they are put into the render array. This would be much simpler, just change some values:

function MY_MODULE_metatag_metatags_alter(&$metatags, $instance, $options) {
  if ($instance == 'MY_INSTANCE') {
    $metatags['title']['value'] = 'My fancy title';

    $metatags['robots']['value']['noindex'] = 'noindex';
    $metatags['robots']['value']['index'] = 0;
  }
}