by Corinne Le Moan.
J'ai réussi à avoir ce que je veux en modifiant : lib/enrolllib.php.
// Add assign or override roles if allowed
//if ($course->id == SITEID or (!empty($CFG->adminsassignrolesincourse) and is_siteadmin())) {
if (has_capability('moodle/role:assign', $coursecontext)) {
$url = new moodle_url('/admin/roles/assign.php', array('contextid'=>$coursecontext->id));
$permissionsnode->add(get_string('assignedroles', 'role'), $url, navigation_node::TYPE_SETTING, null, 'roles', new pix_icon('i/assignroles', ''));
}
//}