You MUST stay within the 150 word limit. I would suggest that you do not even go 1 word over. They specifically make it challenging on purpose. If it was ok to go over by 100 words, they wouldn't have given you a word LIMIT.
If you don't follow the rules here, I believe they would look very negatively upon it. 100 words over is almost TWICE as long as what other people are going to use. I would suggest that you spend a lot of time figuring out how you can say what you want to say in the most concise way possible.
You do not want the admission committee to think you are a rule breaker or that you cant follow directions. I know it is tough, but these essays are ALL tough. They want them to be tough. And they want to see how much command you have over the English language, and how you will put everything you want to say into 150 words.