Change slug when changing custom post type in child

I am trying to change the slug for a CPT in my child theme. I changed portfolio to homepage in my child but my permalink still shows site.com/portfolio/page.html. I want to change it to show site.com/homepage/page.html.

This is the code in my functions.php file I am using to rename the CPT:

add_action( 'wp_loaded', 'wpse_19240_change_home_labels', 20 );

function wpse_19240_change_home_labels()
{
    global $wp_post_types;
    $b = 'portfolio';

    if ( empty ( $wp_post_types[ $b ] )
        or ! is_object( $wp_post_types[ $b ] )
        or empty ( $wp_post_types[ $b ]->labels )
        )
        return;

    $wp_post_types[ $b ]->labels->name               = 'Sliders';
    $wp_post_types[ $b ]->labels->singular_name      = 'Slider';
    $wp_post_types[ $b ]->labels->add_new_item       = 'Add New Slider';
    $wp_post_types[ $b ]->labels->edit_item          = 'Edit Slider';
    $wp_post_types[ $b ]->labels->new_item           = 'New Slider';
    $wp_post_types[ $b ]->labels->view_item          = 'View Slider';
    $wp_post_types[ $b ]->labels->search_items       = 'Search Sliders';
    $wp_post_types[ $b ]->labels->not_found          = 'No sliders found.';
    $wp_post_types[ $b ]->labels->not_found_in_trash = 'No sliders found in Trash.';
    $wp_post_types[ $b ]->labels->menu_name          = 'Homepage Sliders';
    $wp_post_types[ $b ]->labels->all_items          = 'All Sliders';
    $wp_post_types[ $b ]->labels->add_new            = 'Add New Slider';
    $wp_post_types[ $b ]->labels->name_admin_bar     = 'Slider';
}

EDIT: So Googling, I found some code that rewrites the slug successfully, but now I get a 404 page when I navigate to site.com/homepage/page.html. I made sure to try and change my file name from single-portfolio.php to single-homepage.php. Any other suggestions?

function change_slug_of_post_type_portfolio()
{
    register_post_type('portfolio', array(
        'rewrite' => array (
           'slug' => 'homepage',
        )
    )
);
}
add_action('init', 'change_slug_of_post_type_portfolio', 20);