Hi
Unfortunately not,
If all quantities have been posted on an order the system will not allow you to post the order, as it says there is nothing to post
The recommended route would be to use the standard batch job called "Delete invoiced purchase orders"
(You will find it if you search in the RTC search box)
This will delete all orders that have been fully invoiced, possibly run this batch once a week or at end of month to clear out the orders
Hope this helps
Cheers
Nev