Okay, so I'm not sure this is possible but I thought I'd ask.
We're using Paypal Payments Pro (with PHP code), so this is all with using paypal as a merchant account via CURL -- not redirecting the customer.
In our order system, I have two sets of numbers, one is a OrderID which is a primary key and sequential. Orders can be created and sometimes deleted if a person decides not to complete the order. The second number is the InvoiceID which is only generated once payment is actually successful, in order not to generate gaps in numbers or voids. Once a payment is done, I find the MAX(InvoiceID), add 1 and update the Order record.
The problem is with Paypal. I'd like to put the Invoice number as part of the Description since our accounting dept looks at that. But it's circular logic -- I don't have the Invoice number until the Paypal transaction is successful, and once I have it, Paypal is done. So is there a way to go back to Paypal and update that description (or any field) after the fact?