I spent more than a few hours to find and get this working (wish I knew programming). This example code below lets you change the permalink from ai1ec_event to event, and also allows displaying %post_id% instead of %postname%.
Add this to your functions.php and don't forget to click save on your WordPress permalink setting page (you don't have to change anything).
add_action('init', 'ai1ec_event_rewrite');
function ai1ec_event_rewrite() {
global $wp_rewrite;
$queryarg = 'post_type=ai1ec_event&p=';
$wp_rewrite->add_rewrite_tag('%ai1ec_event_id%', '([^/]+)',$queryarg);
$wp_rewrite->add_permastruct('ai1ec_event', '/event/%ai1ec_event_id%', false); }
add_filter('post_type_link', 'ai1ec_event_permalink', 1, 3);
function ai1ec_event_permalink($post_link, $id = 0, $leavename) {
global $wp_rewrite;
$post = &get_post($id);
if ( is_wp_error( $post ) )
return $post;
$newlink = $wp_rewrite->get_extra_permastruct($post->post_type);
$newlink = str_replace('%'.$post->post_type.'_id%', $post->ID, $newlink);
$newlink = home_url(user_trailingslashit($newlink));
return $newlink;
}http://wordpress.org/extend/plugins/all-in-one-event-calendar/
