wordpress change custom post type slug

1function add_custom_rewrite_rule() {
2
3    // First, try to load up the rewrite rules. We do this just in case
4    // the default permalink structure is being used.
5    if( ($current_rules = get_option('rewrite_rules')) ) {
6
7        // Next, iterate through each custom rule adding a new rule
8        // that replaces 'movies' with 'films' and give it a higher
9        // priority than the existing rule.
10        foreach($current_rules as $key => $val) {
11            if(strpos($key, 'movies') !== false) {
12                add_rewrite_rule(str_ireplace('movies', 'films', $key), $val, 'top');   
13            } // end if
14        } // end foreach
15
16    } // end if/else
17
18    // ...and we flush the rules
19    flush_rewrite_rules();
20
21} // end add_custom_rewrite_rule
22add_action('init', 'add_custom_rewrite_rule');
23