What would happen if you "accidentally" left it outside on a freezing night?
In the worst case you would lose your Brewers License and you would be out of business.
Actually the worst case is worse than that. You could go to jail. It is a federal offense.
My limited understanding is that freezing to concentrate ethanol is considered distilling. My information comes from a book about making hard apple cider. They clearly explained that distilling and freezing to concentrate the ethanol is illegal. I have not reviewed the actual law though.
If you are serious about doing this I would consul an attorney. Do not rely upon what someone else is doing. Also, asking a government agency about whether it is illegal or not is in most cases not good enough. If the person who spoke to you is mistaken, that will not protect you from violating the law.