Depends on where you are located!!!
If you are in a northern climate... NOT UNTIL you know the temps will stay above freezing. Clipping a head, especially the ears, could result in frostbite! And the tips of the ears have little to keep them warm except that fuzz. Severely frostbitten ear tips will result in the skin dying, and eventually falling off! I'm sure you've heard of mountain climbers, etc. who have had to have fingers or toes amputated because they severely froze them. Same thing. I've seen a couple horses where this happened. Definitely not attractive!
Those who are clipping heads/necks are
1. doing this late in the winter when threat of frostbite is over, or
2. keeping their horses inside during cold weather, or
3. live in a warmer climate.