It is your head, and the law in your state is of the opinion that it is not worth protecting. So be it. You will have to determine the value of your head. Don't forget to consider your family and friends and how a head injury to you would effect them, short and long term. How would your wife feel having to visit you in the hospital when you are in a coma? And what would the financial burden do to her? Ask her. And be sure to write up a DNR and sign your organ donor card.
Your modifications have changed the structural integrity of the helmet. For the worse. The weather is not a consideration in this. If it is too hot for you to ride, then don't. But don't make excuses. There are many helmets on the market that have great ventilation. I'm sure you can find one.