WordPress - Update postkey once

update-postkey.php

function change_postkey_only_once() {
	$key = 1;
	$option = 'change_postkey_only_once_' . $key;
    if ( ! get_option( $option ) ) {
        global $wpdb;
        $query = "UPDATE " . $wpdb->prefix . "postmeta
                SET meta_key = 'new_key_name'
                WHERE meta_key = 'old_key_name'";
        $results = $wpdb->get_results($query, ARRAY_A);
        return $results;
        update_option( $option );
    }
}
add_action('admin_init', 'change_postkey_only_once');