Hi
NAV does not support editing posted transactions (With a few exceptions E.g. the due date on the customer ledger entry)
The reason for this is so that the system can maintain an audit train on the financial transactions
Having said that there are ways to speed up the crediting and re-invoicing process such as using copy document on the credit to copy the invoice and then copy document on the new replacement order, this means that you dont need to recapture anything
You can also post a sales journal if all you are looking to do is update the ledger on a customer and a direct journal will do the trick
Cheers
Neville