How do I Edit a completed order and Share cart..?

[Coultsy]

We have a client who takes orders with many line items.
Sometimes items are out of stock ad they need to edit the order and add replacement line items.
This can result in a new amount owing.
This process does appear to change the payment status to 'partially paid' which is great, but there seems to be no way to share a link with the user to pay the balance owing.

The 'Share cart' option is not available, I assume because this is not allowed when an order is 'completed'.

I can't see any way to re-open an order or remove the 'completed' status.

I was going to suggest that my client just creates a 'New order' but this is a giant hassle because apparently addresses are not stored against the user so the 'New Order' tool results in no address information.

Does anyone know of a workflow I could suggest to my client?

[lukeholder]

The example templates have an example pay-static of passing in an order number along with the customers email address in order for them to make a payment on an order that is complete but not fully paid. You would make an email that is triggered when you move this order into a status like 'Need final payment' which would have a link to this static payment page. Does this make sense?