Sounds like the rep gave you accurate information. The $500 OBC is tied to the type of category room that you originally booked under. If you change category rooms, you will loose any additional perks (OBC, DOU, free play, etc) associated with that booked rate. You would need to currently have an offers that cover Havana Balconies or suites with any extra perks in order to change room categories.
New casino offers rolled out Jan 4th. You can do a mock booking with any new offers you received and see if they are better than what you originally booked. If the offer is better, then you can rebook at the better offer.
