You asked about the MAIN changes...Well it's the FAT. On Atkins you purposely add fat freely(fat burns fat). Most likely there will be a few days to a week for your system to get accustomed to the change...mine took about a week.
On CAD you do feel like your still on induction on CM meals but with a lot less fat.
There needs to be 24 hrs between RMs...so if you change up your RM from a Dinner meal on Monday to Lunch on Tuesday your body has not had enough time to be 'fooled' and you will take a chance on backtracking... If you know a day or so ahead of time you might have the day preseeding the change as a non reward meal day(3 CMs instead) and have the reward meal whichever meal the next day. The book says to save the changes for only a FEW special days during the year if at all possible. This was so 'sad' for me to realize at first but now I'm resigned to it and realize it's the RULE and if I want to see results I have to follow it. My husband says "This is all rubbish!" But he has a different body and can loose weight easily. Carbs don't bother him at all and it boggles his mind to understand that I'm addicted to them.
Good luck in this woe!
Pat