How do I override headers displayed in permissions tables?
Implement hook_page_alter() and 

function mymodule_page_alter(&amp;$page) {
  if (current_path() == 'admin/people/permissions') {
    foreach ($page['content']['system_main']['permission'] as $index =&gt; $permission) {
      if ($permission['#markup'] == 'Organic Groups') {
        $page['content']['system_main']['permission'][$index]['#markup'] = 'Foobar';
      }
    }
  }
}