Allow Customer To Edit Un-Paid (Open) Orders

As per:

Not a full-on after-sell function, but just to allow the customer to edit an Open order would be sufficient.

Some customers dont understand that they can just view cart later, many place order expecting to be able to add and change later.

We also create orders on behalf of customers and use a "proforma invoice" payment method , which creates an open order. We then edit the order at customers request. Once customer is happy with items in cart they make payment.

It would be convenient to allow the customer to edit order based on Status, Payment method and perhaps User group. This would save us and our customer much time .