By default, once a customer places an order it cannot be edited. If changes need to be made, anad-hoc charge/refund has to be made to adjust the order total. If desired, store administrators can enable the order editing feature, which allows them to edit almost all elements of completed orders.
Different industries and gateways have different rules on editing completed orders. Check with a professional advisor for the requirements for your site.
Enabling Order Editing
To enable this feature, simply set the OrderEditingEnabledSetting to true.
Next, you will be able to navigate the site within a mini-browser window and add/remove items from the cart, similar to creating a new order from the admin console.
Which Orders can be Edited
To qualify to be edited, orders must:
Not be CAPTURED
Not contain gift cards
Not be an Admin User order
Not have recurring items
Not have been previously edited
Not have had the download email sent (if a digital product)
Not been marked as shipped
Not have had the distributor email sent
Not be a PayPal, PayPal Express or Checkout By Amazon order
Not be C.O.D., Purchase Order, Check by Mail, or Request For Quote
Have only a single shipping address (no multi-ship orders)