Adding this: If I can't create an account for someone who can add users, but not change data, could I password-protect my file or tables?
In FM7/8/9/10, the only privilege set that can modify Accounts & Privileges is the [Full Access] account. With that said, there are ways to script the addition of users, enabling, disabling, and changing passwords. And since scripts can be set to run with full admin privileges, you could set something up. Not sure if any of the utilities out there can do any different, like this one:
All file & table protection is taken care of at the 'Accounts & Privileges' window, so there's no extra security layer that can be added.