Ability to cancel a purchase order when goods are no longer required & ability mark a PO as complete without posting an invoice

We need the ability to be able to cancel a purchase order when the goods are no longer required. At present when an order is cancelled the requisition is available again in the Generate Orders from Purchase Requisitions screen. But if goods are not required this means we will have to keep a note to not raise this order again in the future in error. What is needed is a way of marking the order as no longer required that does not effect the requisition and removes the commitment from the budgets. This would also be helpful where we are using a supplier called credit card for people to raise orders where payment is to be made on the corporate credit card. We then process the payments as a VAT payment to the credit card directly rather than adding hundreds of supplier records that may only be used once. For these we then also need the ability to mark the order as complete, but without posting any invoice to it directly as we need the ability to use multiple VAT numbers.