Add adjustments to paid invoices

Inside an invoice, allow people to add adjustments after the invoice has been completely paid. I have thousands of invoices I need to go back and add adjustments to because my predecessor just added payments and write offs but never added adjustments. My current work around is to change the write off amount by $100 or $0.01, as is most convenient, save, add the correct adjustments, and then add back the amount I subtracted from the original write off. As an alternative, I am able to delete a payment or write off completely, add the adjustments, and then add back the deleted payment or write off from scratch, but this is worse. This is a painful process to get around a limitation that feels like it doesn't need to be there.