I think the soda cards on a 7 day trip are about $27 - a good deal. Are your cabins in immediate area? If not, you should try to aim for as early boarding as possible to maximize chances of switching cabins. Of, course, if you just meant switching an adult with a teen, you should have no problem -- the really just do not want totally unsupervised teens sailing -- as long as no excessive noise happens, no problem.