according to MS you can add the DDP up to 4 days of arrival, once the DDP is added you can not take the DDP off the ressie, because the DDP is already charged to your ressie, that you will have to pay for the day you check in.
As far as you being a renter, you will not be able to contact MS, MS is not suppose to give you any info about your ressie. If you contact the resort before you arrive they will only tell you that MS added the dining and that they cannot remove DDP from your ressies and if you have any questions to contact MS. but again you are not a
DVC member and will not be able to contact MS, good luck, personally the dining is well worth the cost and you wont be disappointed.