I don't think DVC points stays are subject to that change fee, as that's more a WDTC package thing. As the DVC rep stated, you have until 48 hours from check-in (note: this is only for DVC points stays!) to make any modifications to the dining plan (add, cancel, up/downgrade, change the # of people).
For WDTC packages, this is 72 hours, and may be subject to fees after 45 days from check-in.