Can I change all prices by changing function zen_get_products_special_price

[perfumbg]

Hello I want to have a 10% discount on featured products but only on CART PAGE so I added on tpl_shopping_cart_default:

<div class="featured-crossale">
            
        
            <?php require($template->get_template_dir('tpl_modules_featured_products2.php',DIR_WS_TEMPLATE, $current_page_base,'templates'). '/tpl_modules_featured_products2.php'); ?>
    </div>

tpl_modules_featured_products2.php is modified acording to use function zen_get_products_special_price2 from function_prices.php where I have copied function zen_get_products_special_price and changed

$special_price = $specials->fields['specials_new_products_price']; 

to

 $special_price = round(($specials->fields['specials_new_products_price'])*0.900); 

When I did that the prices on Fetured products located only on the cart page changed with -10% (the way i wanted), but when I press "add to cart" button, cart page reloaded with adding fetured products but on the regular price not the discounted.

Any sugestions what I'm doing wrong?