No, you can't!
The manifest referenced is for passengers who were already booked on the cruise prior to embarkation day. What the Carnival FAQ means is booked guests must be checked-in no later than 60 minutes before scheduled departure time if they did the online Fun Pass. If they didn't do that then they have to be checked in 90 minutes before scheduled departure time. So to summarize, Carnival has a list of booked guests. They don't add names to it, just take names off for those who didn't check-in in time.
You cannot show up at the pier and get a cabin.