as long as it isn't a credit card reservation which they will charge you for everyone on.
We have travelled with a party of 11 and had only 7 of us show up and it was fine. I have also come as a party of 6 instead of 4. It wasn't a problem. Not to cheat the system to get my ADR. We rarely travel just the 4 of us so sometimes we have more or less people. Family always seems to join at the last minute or change plans so suddenly we're all eating or only half of us are.