I just did this exact thing.
I booked the CP package for 4 at Tutto for my DM, DB, DS and her boyfriend who wasn't sure if he was going to make the trip. When I made the ressie, I asked if going from 4 to 3 would be a problem. The reservation agent told me as long as I took him off the reservation within 24 hours of the actual reservation time, I would not be charged. The moment I found out that he wasn't going I took him off so I wouldn't forget.
As I'm sure you're aware, this package does require a credit card hold. When I made my reservation, I was told (and your CM should have told you) I would be charged for any no shows if not cancelled within the 24 hour reservation window. She did not mention any lower "no show fee", so I assume a no show is charged full price but am not 100% on that.
Enjoy the CP. I've never done it, and am soooo jealous that some of my family members are doing it without me.