Add a dropdown selection to Security Editor > Sales Document Entry, similar to that for Available Shipping Methods, that would allow changing Payment Terms on a Sales Document. Document Payment Terms should still initially inherit from Customer. If possible, also allow changing terms back to the Terms on the Customer record in addition to the selection(s) in Security settings.
Example: allow Sales to change any document to CREDIT CARD or ADVANCE PAY, as well as changing back to the customer's default terms.
Thank you for this idea! We've created a case for investigating further.