If this is not already on the radar, could it be added to the developer's listing for future enhancements, please?

I'm not looking for exactly what is addressed here, but I'd like to have the ability to put a post-it note on an invoice for when something changes.  For example, an order for $159,000 included a discount on certain items.  The customers PO requires line by line amount matches.  The customer mis-calculated the discount which makes matching the line item totals impossible other than by using the customer's numbers.  When I look back at the invoice, I know something is wrong when compared to the contract.  I would like a post-it or pop-up note that shows on the screen, but not on the actual invoice when printed.