Change your diet whenever you aren't getting results
What I mean is that you should be keeping a constant gauge of your progress, things such as weight, body measurements, lifts and then use that determine if you need to change up the diet. There is no real need to do something completely different if you are happy with your current diet. If 40/40/20 is working for you and you cutting 1 or 2 a week then when you stall just lower the calories. There is no need to say, well sorry carbs you have to go. Lower your total calories, increase your cardio or make some other change to increase your calorie deficit.
I would recommend
http://www.alanaragon.com/my-book.html (there is a whole chapter on coming up with number of calories to consume)
to get an idea on how many calories you actually need, and coming up with a plan.
Or if you want to save yourself a ton of time, just sign up with the clown,
http://www.flanutrition.com/services.html .
I have been with him since mid-January and I am down 24 lbs, while maintaining all my strength. Sure I look skinny (6'1' 168, 28.5" waist), but I hear he runs a mean bulk as well
Don't fall into the trap of thinking you need to "shock" your body and be miserable to get results. I would highly recommend either of the above sources to get a game plan that has some science behind it.