Example usage

customroute.php

<?php
/**
 * @author      SDKiller
 * @copyright   Copyright (C) 2015 SDKiller, http://jexy.ru. All rights reserved.
 * @license     GNU General Public License version 2 or later; see LICENSE.txt
 */

defined('_JEXEC') or die;

require_once dirname(__FILE__) . '/MyCoolRouter.php';


class PlgSystemCustomroute extends JPlugin
{
    /**
     * @throws Exception
     */
    public function onAfterInitialise()
    {
        $app = JFactory::getApplication();
        if (!$app->isSite()) {
            return true;
        }

        //set router override

        /** @var $router \JRouterSite */
        $router = $app::getRouter();

        $crouter = new MyCoolRouter();
        $router->setComponentRouter('com_content', $crouter);

        return true;
    }

}