Default Num Lock is on or off controlled in the bios of a computer. In enterprise environments there is usually a bios password. So users aren’t allowed to change the default behavior of Num Lock (on or off).
Windows has a built in trick for this.
When the computer boots and the login screen is displayed set Num Lock to the preferred status. Then DON’T login but restart/shutdown the computer. The next time Num Lock is just the way the users want’s it 
Q: Is is possible to let users change the default Num Lock status with a BIOS password?
A: Yes, set the preferred status at the login screen and reboot the pc.
There is even a solution for doing this in the registry.
- Start the registry-editor.
- Go to HKEY_USERS\.Default\Control Panel\Keyboard.
- Change the value of InitialKeyboardIndicators from 0 to 2.
