With a
DVC rental, the member making the reservation controls all aspects of the reservation until you check-in at the resort. Any roon requests or Dining Plan need to be managed thru the member calling
DVC Member Services. Some have reported adding DME by calling Magical Express directly - so that might be an option - but anything involving the reservation that requires going thru MS can only be done via the member who made the reservation.
Even if you are a DVC Member, but renting from another member, you will need to go thru the member who controls the reservation.