If its important to you, make the time to sort it ASAP. Go to the dealer, if you cant go there ring them. Your a customer who is spending their hard earned money, and whatever the answer is, delaying will only make it more difficult.
Tell them you have made a mistake, the worse that can happen is they can say tough its too late. The last thing that is going to help you is if you start quoting someone on here who says its no problem to change the order. Just be clear, honest and firm with the dealer to find out what your options are.
RBW.