Change Slug of a Custom Post Type

In the code you posted, the filter ctc_post_type_item_args gets applied to the $args array before it is passed into register_post_type().

Putting a function into your themes functions.php and hooking it to the filter should do the trick:

function wpse_191003_ctc_post_type_item_args( $args ) {
    $args['rewrite']['slug'] = "your_new_slug";
    return $args;
}
add_filter( 'ctc_post_type_item_args', 'wpse_191003_ctc_post_type_item_args' );