Thanks for bringing this to my attention. There had been some debate on which way this would be handled, and at the most recent meeting I'd been to, it looked as if the decision was made to require additional mileage if a customer had upgraded prior to the new rules and was now making a change to flights after the fact.

After checking with a manager at Mileage Plan, it has been changed as you describe; customers who redeem miles for an upgrade will be able to use that upgrade without additional mileage deductions, even if changing dates after the fact.

The thing to keep in mind is that the "old" upgrade information is retained in your passenger name record (PNR) for the dates you're currently booked, so if you make changes to the dates, be sure you do so prior to those first travel dates taking place. Otherwise, the agent will have to create a wholly new PNR for you, and the old info will be lost.