In the same way that you don't become the slave of any other rules and laws.
If you walk through your city at night and there are no traffic and no children to learn from your bad example, you cross the street although the traffic light is red. If your plot has an internal logic that contradicts three act structure, you follow your plot.
Writing instructors often use examples. They analyse a novel, find the three act structure, and then use this novel to illustrate their formula. But if you actually take up that book and read it for yourself, you will usually find deviations from and contradictions to that formula. Plot formulae are a simplifictation of real novels, just as the rules of etiquette are a simplification of real-life human interactions and don't always apply.
Beauty, as psychologists have recently found, is not perfection. Perfection is boring and unexciting. Of course symmetrical faces are generally found more attractive than unsymmetrical faces by the average person. But for a specific individual what is most attractive are specific deviations from perfection.
Formulaic fiction is utterly uninteresting. What kicks you in the balls is the deviation from the expected (as you can easily experience with my choice of words here).
You have to get the direction of the chain of cause and effect right here. Good fiction is not constructed after a formula. Formulas can be found if you simplify good fiction. Why? Because life itself is perceived in retrospect by human beings as events leading up to a culmination and turning point, after which there is an aftermath of returning life to normal. Formulas can be found in stories, because they reflect how human beings make sense of their lives. So if you write a story that makes sense, it will always contain elements of a formula. You don't have to construct your story around that formula.
The purpose of the formula is to help you get an outside view of your own writing. You know the story you want to tell, you understand what's going on etc., but will your reader? You could simply let your text rest for a year or two and then come back to it with a clear mind, but since you are in a hurry you use a formula to compare your text against. The formula is the average, "normative" reader. If your text works for him, it does make sense. But no more. It might not be good, it might not be entertaining, all you know is that it works on the most basic level. So don't trust the formula beyond what it can do.