Any way to set default template for all pages in a container?

<?php
global $content;
$e = &$modx->Event;
$containers = array(1,2,3); // container IDs for custom template
$custom_tpl = 12; //custom template ID

switch($e->name) {
  case 'OnDocFormPrerender':
    if(($_REQUEST['pid'] > 0) && ($id == 0)) {
    	if(in_array($_REQUEST['pid'], $containers)) { 
    		$content['template'] = $custom_tpl;
    	}
      	elseif ($parent = $modx->getPageInfo($_REQUEST['pid'],0,'template')) {
        	$content['template'] = $parent['template'];
      	}
    }
    break;

  default:
    return;
    break;
}
?>