Hi
I believe you can only lock the Factory Reset button but not the Restart button.
One option if you have access to the codec and can login to the device via web browser or control hub | Device | Configurations | All Configuration | UserInterface | Settings Menu set to Lock and then they wont be able to factory reset the device, but they can restart the device.
I'm think a general user wont or shouldn't be messing with this setting but maybe in your case they are.
Thx
ashish