Prestashop 1.6: Allow customers to edit order in front office before shipped

Hi, In Prestashop 1.6.1.13 we need add the functionality where a customer can edit their order in the Front Office before it is changed to 'Shipped' status. After 'Shipped' status, it is no longer able to change. (there is already a cronjob which marks the order as shipped automatically the day before delivery date). For example, the customer might want to add more products, remove some products, change quantities or cancel the order completely. As they are updating the order, the new total and difference between the two orders should be calculated for the customer. We already have the function for customers to cancel the order completely. When a customer edits the order, they should get a new email confirmation and invoice with the updated order. We also need to account for the difference in payment. We use SagePay as our main payment service - so can use the REPEAT or PARTIAL REFUND API requests for the difference in order value. The new payment/refund confirmation will need to update in the ps_order_payments table so the payment on the order is validated. There is also a credit account module (wkcreditcheck) that we have installed - so the payment will need to be reflected on the customer's credit account balance in the module too (if they choose this payment method). We also have PayPal and Amazon Pay installed - but I think we should not make those available for edited order payments. See sample documentation for information on the functionality required. Please message with any questions. Thanks, Rhys