Those should prevent the addition of personal accounts moving forward. The issue is that if they have all ready added that personal account, this actually blocks them from signing out of the personal account and will block them from their CPS accounts. At that point, you will have to instruct them to reset Profile Settings (chrome://settings/resetProfileSettings). That resets them back to default (it doesn't lose bookmarks, it just signs them out of everything). It is a pain, but it works.