That aspect ratio change would throw off your speedo a little bit, but wouldn't affect the alignment. I have 245/35 x 19 in front and 275/35 x 19 in the rear. Alignment doesn't change and the speedo remains fairly accurate.
Traction control will become more sensitive ,ie. activate easier and more often. Since the new rear tires will be spinning faster at any given speed ( in relation to the front tires) (due to the smaller overall circumference of the new tires) than what it is calibrated for, it will "think" the rear tires have lost some traction and are "spinning" even when they are not. Many threads on this.