Great technique! What I've noticed is that catching your negative thoughts and replacing them by the ones you prefer is also a great way to become less identified with the mind. Which in turn makes it more and more easy to choose your thoughts consciously, to make the mind your instrument instead of you getting carried away by it all the time. So my experience is - doing this becomes more easy in time, evolves you into a lighter and ligher and happier space as you move along!