Shortening stay with expired offer

[Djscarlette]

Hello all,
Does anybody know....
I have a room booked with the fall discount offer. I have the room booked one day past my flight home hoping Southwest will have a price decrease so I can extend my stay one day. The fall offer expires on August 31. Do I have to drop my extra day before the offer ends to keep my offer on the days I am going? Or is it ok to drop a day and keep the offer even though the offer is expired. I am not trying to add on days or change dates so I didn't know.

Thanks!!