You are doing it the wrong way. Do it as followed:
A) Easy but not recommended Way:
1) Open Controllers/IndexController.php
2) Modify function initContent as below :
public function initContent()
{
parent::initContent();
Tools::redirect('index.php?id_category=10&controller=category');
$this->context->smarty->assign('HOOK_HOME', Hook::exec('displayHome'));
$this->setTemplate(_PS_THEME_DIR_.'index.tpl');
}
B) Recommended Way:
1) Copy Controllers/IndexController.php to override/Controllers/ folder 2) Open the copied file and edit as below:
class IndexController extends IndexControllerCore
{
public function initContent()
{
Tools::redirect('index.php?id_category=10&controller=category');
}
}
3) Save the file and go to cache folder. Find class_index.php , if it is there then delete it. Then check the site if it works fine.
Notes :
1) The above code is to give you idea, it may or may not work. Please do adjustment according to your needs.
2) In latest versions of Prestashop, all classes are indexed in the class_index.php file. so if you made any override of a controller or class, it may not work until you delete that file. When a new request is made to server, PS automatically regenerate that file for you.
Hope this will help.