Edit order to show refund or part refund

Cust purchases 4 items which we dispatch. He then decides – for whatever reason that he needs to return one of them. If it is faulty we will replace (zero rated invoice) and refund return postage (we would need to do this as a spare part), or refund no re-stock fee if he chooses.

Ideally we need to do a refund against an original invoice number for tracking purposes. We need to do a minus part (so that it stock gains the part)
If he is returning a part because he changes his mind, their would be a 10% re-stock fee.

the edit orders hack doesnt seem to work on our site - BUT we do have a huge amount of hacks on our store to make my boss happy - anyone got any ideas on this or do I go the custom hack route on this ??