Hook for altering secondary local tasks
$primary = menu_local_tasks(0);

$secondary = menu_local_tasks(1);


See: http://api.drupal.org/api/drupal/includes%21menu.inc/function/menu_local_tasks/7

It's actually not a hook, it's just a function that gathers the items while in context.

There is a hook to alter the items: http://api.drupal.org/api/drupal/modules%21system%21system.api.php/function/hook_menu_local_tasks_alter/7