A revo-version of Inherit First Child Template?

Is there a plugin for Revolution that let you Inherit First Child Template when you create a new document?

I have now gotten this far:

if ($modx->event->name = 'OnDocFormPrerender' && $mode == 'new') {

$parent_id = $_REQUEST['parent'];
$array_ids = $modx->getChildIds($parent_id, 1, array('context' => 'web'));

if(!empty($array_ids)){
$child_id = $array_ids['0'];
$child = $modx->getObject('modResource', $child_id);
$tpl = $child->template;
}

}

Now I have to set the new documents template to $tpl. Anyone know how to do that?

I found out that I could do the things I wanted with this plugin with Form Customization. Is that the correct way to do it?