Example of a plugin extending the Sizeable_Person object.

szbl-person-plugin.php

<?php
/*
Plugin Name: Extend Sizeable Person
Description: Adds post thumbnails, excerpts and page attributes to People post type. Also, sets URL slug to /people/ instead of /szbl-person/
Author: theandystratton
Version: 1.0
License: GPL2+
*/
add_filter( 'szbl_people-post_type_args', 'szbl_people_filter_post_type_args' );
function szbl_people_filter_post_type_args( $args )
{
    $args['supports'] = array( 'title', 'editor', 'custom-fields', 'thumbnail', 'excerpt', 'page-attributes' );
    $args['rewrite'] = array( 'slug' => 'people' );
    return $args;
}
?>