Credit Note & Debit Note

Would be good if there is options to add in a credit note or a debit note for invoices so that if there are changes to invoice, we don't always have to cancel and re-do it. It gives a better history of accounts

I may develop such an app. Can you elaborate plz? Maybe with screenshots.

Basically rather than having to edit the invoice amount or delete the invoice when an amount is inaccurate. THere is an option to create a credit note or debit note to either decrease or increase the invoice. Credit note being to reduce the original invoice amount and Debit note to increase the original invoice amount. 

Was this ever developed?

I fully support that idea. It happens that an invoice is created but the wrong customer is billed. That customer then needs to be sent a credit note for the same amount, indicating that the payment expected is reversed and the credit note married to the incorrect invoice. Afterwards a new invoice is generated for the customer.