Custom price calculation for specific product

[spaceace17]

Hi to all, I'm writing here to find a solution for a big trouble in my PS 1.5.x store.
I need to add an extra cost to a specific produtc, which does not change with the product amount.
So if you order 1 unit the extra cost is $10, and remains the same if the ordered unities are 10, 100 or 1000.
PS does not allow an option like that, so I'm considering to do some customization in PS core.
I find a line of code in classes/Product.php which can do the job:
 

        // Attribute price
        if (is_array($result) && (!$specific_price || !$specific_price['id_product_attribute'] || $specific_price['price'] < 0))
        {
            $attribute_price = Tools::convertPrice($result['attribute_price'] !== null ? (float)$result['attribute_price'] : 0, $id_currency);
            // If you want the default combination, please use NULL value instead
            if ($id_product_attribute !== false)
                $price += $attribute_price;
        }

Can I add something like
 

if (product_id = 44) { $price = $price + 10; }

to add a certain value to a specific product?