On this document it's explained how to prevent the Users to change the Scalability Server their machines are pointing to.
Client Automation 14.x
In order to change the Scalability Server that manages a specific machine, the following command can be executed from CMD:
caf setserveraddress <new_ss>
The way to prevent this command to be executed, the following policy can be modified:
DSM > Agent > Common Agent > Common > Scalability server address
If this policy is set to "Centrally Managed" (by right clicking on top of this Policy), the User will see that the command "caf setserveraddress new_server" won't be executed.
Instead of modifying the Default Computer Policy, it's recommended to create a new Policy and apply that policy to the desired Agents.