It is impossible. I'm sorry, no matter what you do, you'll have to live with your decisions. There is no way of sending any information to the past (see time paradoxes and other threads, they say the same). That's how the universe works. I even don't think the future is existent until you have passed it now. I mean, there is no existence of anything of tomorrow until tomorrow becomes a now. The same can be said at July 4th when you made that decision. You are in the process of making the regret now. We have to live with it because otherwise, if the future is already existing, then that means we are all just characters in a book. This means we may think we have a decision that can change any time we change our mind but you know that when you flip to the next page, the same thing is there, no matter how many times you do it. The future is better seen as undone, because that way, we live in the present and make real decisions now. And getting regrets from time to time is a small price to pay.