With the last release of Store, the ability to edit an order within the control panel was added. Is there a hook which can be used to do something once an order has been updated?
Depend on what are you trying to do. A safe hook is on the store_order_recalculate_end hook, since the $order object is passed and you can check the status.
When you update the order in the CP the last thing that happens is that hook.