This question has been answered by schouinard. See the first response.
<?php // Check Event if ($modx->event->name == 'OnDocFormSave') { $resource = $modx->getObject('modResource', $modx->event->params['id']); if($resource->get('template') == 8){ $resource->set('uri', $modx->makeUrl($resource->get('parent')).'#'. $resource->get('alias')); $resource->save(); } }