Firstly, I'm sorry, but every major hotel in French Polynesia does this. You'll be paying for it whether you eat it or not..... They won't cancel your booking, but it is a condition of your booking, and if you don't accept it you should cancel.

Secondly, while I think that Bora Bora is the greatest, most spectacular destination in the world, what on earth possessed you to go in the middle of the rainy season? Is it too late for you to change to a time of year when the weather is better (Easter to October), or else switch destinations to somewhere which has decent weather at Christmas?