I carry that to buying one tire if my car needs only one tire and it gets installed wherever the bad tire was located and have never had a problem in the winter snow.
The instructions for putting the best tyres on the back are made for emergency conditions, not normal driving. Under normal driving conditions, including snow and ice, it does not really come into play. It only comes into play under emergency conditions when you are loosing control of your car. Many people are lucky enough that this never happens to them, but when it does it is most often very serious.
The car manufacturers and tyre manufacturers all agree on this issue and they have the test tracks to safely test such issues.
Everyone please remember that under emergency conditions your car will not respond as it does during normal driving.