One of the little known issues about icing is that the approval is only for droplet sizes smaller than 50 microns - that's the size of a 0.5mm mechanical pencil. This is pretty small.
Anything larger than 50 microns is freezing precipitation, and there is no approval for flight in that.
Not many people know this.
Freezing precip is much nastier than the stuff that is tested and approved.
Even fixed wing aircraft have serious problems with freezing precip.
As far as cold weather as separate from icing, lots of helicopters are cleared to the colder temps.