Just the opposite. Normally the rear cylinders go leaner without the power plate. So theoretically you'd be better off without the plate in cold weather. : ) But I don't think you'll have to worry about temps getting too cold with a dutt neck stock IC that's listed in your sig. You'd need a large IC that can get the temps down. And if you are running the turbo in your sig at high boost the temps out the turbo are going to be pretty high. You could probably run in -20 weather before you'd reach the inlet temps that the large turbo/FMIC combos are seeing and it's debatable if it's even an issue with those combos.
And just to be clear, what people are theorizing about the cold weather effect with alky would only affect those people who are doing wideband correcting of their fuel. So the theory is...is real, it would richen up the rear cylinders only, give a false rich reading, the chip/ecu pulls fuel, the front cylinders go lean when the fuel is pulled, boom. Now there is no measured data saying how much the wideband A/F reading would change with the effect as it is pure guesswork. So if you are not correcting and run the same amount of boost in the colder weather it shouldn't affect you. Now if you run more boost because of the cold weather you will need to add more fuel typically. So if you are not correcting for this you'll get in trouble anyway, which seems to be the most common fault in cold weather.