This is the first time we have received such a request: to blank the screen but not the mouse attached to the computer whose screen you just blanked 🙂
The non-disabling of the mouse is not a configurable option. The majority of our users use remote screen blanking as a security feature, to prevent people in the vicinity of the computer from seeing and interacting with the computer. Although splitting the mouse input from the blanking of the screen can probably be done, it would create confusion in our honest opinion and is not what most NoMachine users expect.