That would also remove some actual beer - what freezes off tends to be water and whatever can be solid at that temperature. Things like sugars giving body to the beer and what has a higher affinity to the concentrated alcohol solution would remain in the liquid phase.

For example, this is how brewdog does their very high alcohol beers like tactical nuclear penguin.

Though I would recommend to the OP to check out the brewdog recipe for Nanny State. That could be a starting point.