How can set a custom action with a custom attribute selected in form?
It is possible to use the $_POST array in the custom php code, which can be called in the action, which is assigned to the vbo action!
The page to show the view with the vbo fields is: /node/%node/add_person_to_event, so arg(1) is the nid of the event.

So my custom action code is:

$status = $_POST['status'];
$event = arg(1);
foreach ($_POST['views_bulk_operations'] as $key-&gt;$vbo_nid) {
   build_relation_person_event($event, $vbo_nid, $status);
}