What I need here is, whenever the user change the font using Control panel, an alert should be made to the user and the font should not be changed.
I am confused why the method the user chooses matters.
Why is it a problem if they use the Control panel but not the Character panel?
I don't think you can achieve this with scripting.
With substantial effort, you maybe able to detect when they change a font and pop up an alert, but it is pretty difficult.
It would be more doable but still hard in the C++ SDK.