MODx Wayfinder to limit certain pages

Question

On my current page I have wayfinder defined in a snippet that if this is a top level item, return it's child docs. If it's a child doc, return it's siblings:

<?
$id = isset( $id )? $id: $modx -> documentObject['id'];
$parentID = $modx->getParent($id,1,'id');

$startId = $parentID['id'];

if ($startId == 0) {$startId = $id;}

$output = $modx->runSnippet(Wayfinder,array('startId' => $startId, 'level' => '2', 'outerTpl' => 'int_outerUL','innerTpl' => 'innerUL', 'firstClass' => 'first' ));

print $output;
?>

However I do realise there is a limit parameter that can be put in process here but I am trying to limit the pages to only take effect on a certain page. I am still a modx noobie so any advice would be greatly appreciated.