a modified reservation that was originally made today or in the past, will get free parking. As long as the original reservation number exists, it will be honored.
Change resort, modify party size, changing the stay dates, adding a discount, are all forms of modification and won't affect free parking eligibility.
After today...........If however you CANCEL the reservation, and even book for the exact same stay dates, THAT will put in in the "pay for parking" category.
To cover your bases, print out a copy of your present reservations and the present policy page. That documentation might come in handy.