Off on a tangent perhaps, but:
I've found little value in being able to edit an order; from my perspective, once an order has been placed/confirmed, that is the order... editing it and sending out other invoices with the same invoice number just isn't, well, proper. The audit trail gets muddled, and the customer is liable to get confused. And it breaks up the whole checkout process.
I edit the basket contents to add custom items which are moderately hidden in the catalogue (eg installation fee or extra postage fee, both "normal" products at £1 each) and negative item quantities for when a customer returns an item. (Negative values require core file edits).
Then, all "negotiation" is performed before the order is actually placed.
But, and it's a big but, I use a MS Access interface to the database to do this - to edit the basket and other stuff. And even then it's not perfect, due to the way Zen Cart stores the basket contents in the session and/or database...
Sorry if this doesn't particularly help the OP, but I do see a need to edit the basket.
Unless I've overlooked a simple alternative?