I think the closest you will get is to go to invoice data entry. Enter using the same invoice # and select the option for adjust. Change the header comment. Update. This will cause there to be a secondary entry for the invoice (you will see an invoice record and an adjust record). The adjust record will have the changed comment. I'm not sure how this will come out on reports.

Theoretically you could do the change for detail lines, but once again I don't think it will replace the original lines, just add additional lines.