$pretemplateCrumb .= '<a class="'.$crumbClass.'" title="'.$title.'" href="'.$modx->makeUrl($c['id']).'">'.$text.'</a>';

заменяем на:

if ( $c['id'] == $modx->config['site_start'] )
$pretemplateCrumb .= '<a class="'.$crumbClass.'" title="'.$title.'" href="'.$modx->config['base_url'].'">'.$text.'</a>';
else
$pretemplateCrumb .= '<a class="'.$crumbClass.'" title="'.$title.'" href="'.$modx->makeUrl($c['id']).'">'.$text.'</a>';