One caveat with csutil is that the password will be reset - you can not change the group without affecting the password. If you know the passwords of each account to be moved, you won't have a problem. But on existing accounts where users havce changed their original password, you will have a problem.
I would suggest you look into using the CSDBSync capability which is similar to CSUtil, but has many more capabilities and is just as easy to use, once it has been set up.
Set up processes are in the user guide and work very well.
