Yes. We can enable/disable at runtime from Unity C# script.

Answer: https://stackoverflow.com/q/51323819/3185013

Disable the Virtual Buttons Menu in the ARCamera's Inspector panel.

one more question.,

how i can remove white line(square line)  in virtual button at runtime ?

There is a SetEnabled( bool ) method on the VirtualButton class - https://developer.vuforia.com/resources/api/class_virtual_button.htm

But this requires that you deactivate the associated dataset, which you'd have to subsequently reactivate so that the other buttons are enabled.

A less costly and complex approach would be to unregister the event handler for the VB - https://developer.vuforia.com/resources/api/class_virtual_button_behaviour.htm

But the simplest approach may be to handle this button logic in the event handler itself, by storing the name of the last VB that was pressed and responding accordingly for subsequent OnButtonPressed events arising from the VBs. For example after the red button is pressed, you would ignore presses from red and yellow. After the blue button is pressed, then you ignore subjequent blue presses and and only respond to red and yellow presses. If your logic is path dependent, then you could store the history of presses in an array.