Customize Prestashop Module

Hi, the customization required is for the Prestashop module Auto Add to Cart by 202-ecommerce ([login to view URL]). The required change involves the front-end side: at the moment, it’s not allowed to increase/decrease the quantity for more than one item per time. Therefore, in the case of two linked items, the user is forced to increase/decrease the quantity for each of the items he wants to purchase. What we want to achieve is that it’ll be created a correspondence between the items (which have previously been linked together in the back-end side of the Auto Add to Cart Module) so that each edit in the quantity amount of one item is immediately repeated on the corresponding item. For example: if a customer decides to purchase the “Product A”, in the cart appears a row for the “Product A” item and another row (which is a one-time cost for the “Product A” item). If the customer wants to buy 2 of “Product A” items, he’ll have to increase the quantity for that item to 2 and, automatically, that same quantity must be set for the one-time cost corresponding to that item. The Prestashop version in use is 1.4.7.3