How do I reverse a method call?

This might be a strange ask. There’s the method AccelTimer() that I want to initiate in Update(), but if a button is pressed, I don’t want AccelTimer() to be called. Is there a clean way to go about this? Thank you!

        AccelTimer();

        if (Input.GetKey(KeyCode.Mouse0) || Input.GetKey(KeyCode.Mouse1))
        {
            !AccelTimer(); //Or whatever it may be. I'm not sure how to do this part.
        }
        else
        {
            AccelTimer();
        }

You don’t want to reverse the method - you want to reverse the condition on which the method is called:

     if !(Input.GetKey(KeyCode.Mouse0) || Input.GetKey(KeyCode.Mouse1))
     {
         AccelTimer();
     }

what if the method calls its self like OnMouseDown()?