Perform Action on Ticket Status Change

<?php
add_filter( 'wp_insert_post_data', 'wpas_custom_status_change_notification', 10, 2 );
/**
 * Check if the ticket status has changed and, if so, maybe send an e-mail notification if the new status required one.
 *
 * @since  3.0.0
 *
 * @param  array $data    Post data
 * @param  array $postarr Original post data
 *
 * @return array          Modified post data for insertion
 */
function wpas_custom_status_change_notification( $data, $postarr ) {

    // Make sure we only work on tickets and not other post types
    if ( ! isset( $data['post_type'] ) || 'ticket' !== $data['post_type'] ) {
        return $data;
    }

    // We're not interested in tickets being trashed
    if ( 'trash' === $data['post_status'] ) {
        return $data;
    }

    // Not interested in auto-drafts either
    if ( 'auto-draft' === $data['post_status'] ) {
        return $data;
    }

    global $current_user;

    // Make sure the current user has the capability to edit a ticket
    if ( ! user_can( $current_user->ID, 'edit_ticket' ) ) {
        return $data;
    }

    // Get the registered custom status
    $status = wpas_get_post_status();

    // Make sure the new status is a registered one
    if ( array_key_exists( $_POST['post_status_override'], $status ) ) {

        // We only want to send the notification if the status has changed and if a new reply is being posted
        if ( $postarr['original_post_status'] !== $_POST['post_status_override'] && isset( $_POST['wpas_post_parent'] ) ) {

            switch ( $_POST['post_status_override'] ) {

                case 'status1':
                    // Do something when the new status is "status1"
                    break;

                case 'status2':
                    // Do something when the new status is "status2"
                    break;

            }

            // If you want to perform the same action whatever the new status then remove the entire switch() block and add your action here

        }
    }

}