On a package however, you can not modify to make the price lower, only higher, that is my previous experience with them. I am strictly speaking for room only reservations.[/QUOTE]
I called recently, inquiring about a package, and was told by the CM that they would modify to a lower price if a better deal came out later. The only catch was:
1. The new promotion price would be reflective of the current prices. So if you booked way in advance and the ticket prices changed in the meantime, your discount may be a few dollars less.
2. You can apply the discount only if the type of accomadation you are requesting is still available. For instance, last year we booked a Standard room, a better deal came out, but no standard rooms were left on the days we wanted to go, so we upgraded to concierge, which was available, and ended up actually paying almost the same as the standard room (but with an upgraded accomodation).
3. You can modify your reservation to reflect the promotion up to 30 days before travel without penalty. Within 30 days there are some tiered penalties for changes ($50 - $100) but I don't recall the time frames for each. However, if you can save $300, a $50 change fee is still worth it.
I was told the above applies whether booking through WDTC, Costco or AAA. There may be others, but I only asked about those three.
Now I realize we sometimes get conflicting information when talking to DLR reservations, and misundertandings can happen easily, so I would make sure to confirm this with a CM personally and ask specific questions to your particular trip.