Order editing is now available on Shopify
Shopify previously did not allow editing orders after payment. If you want to do that, you must use a Shopify apps from 3rd party. Actually, the apps will cancel previous orders and create new order with the new adjusted values. But now, you can now make changes to what is sold on an order without any clunky workarounds, like canceling an order and creating a new one.
After an order is paid, you can edit it by adding items, removing items, and adjusting item quantities. Also you can change an item or if you need to add or remove an item. For example, a customer might want to change the size or color of an item on their order.
You can edit an order only if it was placed less than 60 days ago. You must also be the store owner, or have a staff account with the Edit orders permission enabled.
The total cost of an order is updated as the order is edited. If the cost of the order changes, then you need to charge or refund your customer the cost difference.
To edit an order, simply click the Edit order button at the top of the Orders page.
From here, you can add or remove items (including custom items) or adjust the quantity of items. You can also send update notifications to your buyers and include a checkout link to collect additional payment on orders that increase in value.
Please note that this feature is not yet available for Plus merchants.