If there are certain configuration values that must never change, they should not be surfaced in a GCV.
All information in a GCV can be easily changed or tuned. To keep certain configuration values and implementation details from being changed, add this information directly into the code. Everything that an administrator should see and be able to change should go into a GCV. Everything that only a developer sees or changes should go directly into the driver policy code.
The only reason to add a static value to a GCV is if it is used in many different places and it does not make sense to add it directly to the code.