WordPress: hook pre_get_posts for custom posts per page

<?php
//hook pre_get_posts for custom posts per page (brute force rs)

    function custom_posts_per_page( $query ) {
        if(!is_admin()){ //afetará somente o front-end
            if ( $query->is_category && $query->query_vars['category_name'] == 'SLUG-DA-SUA-CATEGORIA'){
                $query->query_vars['posts_per_page'] = 5;
            }

            if ($query->is_post_type_archive && $query->query_vars['post_type'] == 'SLUG-DO-SEU-POST-TYPE'){
                $query->query_vars['posts_per_page'] = 3;
            }
        }
    }
    add_action( 'pre_get_posts', 'custom_posts_per_page' );
?>