DVC Packages on Disney Site

[jellydoughnut]

Every now and then when I put dates in the near future on the Disney site, I get package rates that include DVC resorts with pretty good rates for a family of 5. When I click next, the tickets are already included. Other times, all I get is nightly rates on that first page and then have to click next and add tickets. Does anyone know the trick to this? I want to be able to choose to see packages (including DVC resorts) or not...

Also, if I book at a regular nightly rate with tickets so that I can book my dining and Fast Pass reservations, can I later change that reservation with no penalties to grab one of those DVC resort deals?