The things you can't do directly with Disney: change your room. change your dates. change people on the reservation (probably). Make payments. From what was said above, and I can't remember specifically enough to contradict it, book transportation.
The things you CAN do: dining, inform them of a CPAP and request extension cord and distilled water for it, palo/remy, excursions, checkin, get PAT, etc etc etc.
If you like messing with your actual reservation, then giving up the control probably won't be happy for you. If you don't change big things, then you'll probably never even notice it.