In AR how to make invoice corrections?

We are on 11.5.10.2. I need inputs, suggestions on the following process.

We create invoices based on estimate and send to customer. Customer gives us the feedback and we need to correct the invoice accordingly (Of course after verification). Since many times the pament terms is over by the time of correction the invoice becomes unavailable for correction. We need the facility to correct the invoice as and when required as well as update the line (item description).

Please throw your suggestions (except changing the business process!!!!).

Thanks.

Anil