Change Wordpress theme only for one user, ex. for developer.

<?php
// Vladimir Zhelnov // neatek.ru // neatek.pw
// create a new folder in wp-content/plugins
// create a new file index.php
// some changes&copy&paste

add_filter('template', 'change_theme');
add_filter('option_template', 'change_theme');
add_filter('option_stylesheet', 'change_theme');

function change_theme($theme) {
    if (get_current_user_id() == 4) { // here is 4 is user_id of Developer
        $theme = 'here is a name of the folder which contain new theme files.'; // theme for only one user for develop a new theme
    }
    else {
        $theme = 'here is a name of the folder which contain standart theme files.'; // standart theme for all users
    }

    return $theme;
}