The unicorns shouldn't stop using "Frostyshivers".

[Shady Mist 55]

There is still a problem with the unicorns now using "Warm Wishiehoof" instead of "Frostyshivers". If the unicorns only use "Warm Wishiehoof" it would cause the opposite effect, instead of have it be freezing, it would make it like a desert. What they should do is alternate, whatever pony says "Warm Wishiehoof" the pony they're talking to should say "Frostyshivers" back, or visa versa. That would cancel them out and not cause any effect on the weather.

[Misty Shadow 7,862]

Saying "Warm Wishiehoof" cancels out the freezing cold weather in the winter. "Frostyshivers" makes the cold worse while "Warm Wishiehoof" makes the cold more bearable. There already is a balance in place. 

[cuteycindyhoney 13,307]

I still think "Frostyshivers" sounds like a yummy summertime beverage!