Yes, my wife has made many dishes reducing mead exactly as you are saying. Spectacular stuff, let me tell you. ;D Beats the pants off grape wine any day.
Mead concentrates in the freezer because the water freezes, but the alcohol and flavor compounds don't. You pour off the alcohol and throw away the ice. This usually results in about 2-3x ABV, depending on how cold you can get it. The technical term is "fractional distillation", and the BATF treats it exactly the same as normal distillation. That is, a $5k fine and 5 years in prison.
The danger is that in concentrating the alcohol, you also concentrate the methanol. In normal distillation, you throw the methanol away. Fractional distillation was a very common practice in New England in times past with cider, and the concentrated methanol lead to a condition known as "apple palsy". Not good.
Edit: Oops, posted at the same time as David. HI DAVID!!! ;D
Yes, distillation is illegal, except for a couple of more-or-less irrelevant exceptions. Mere possession of a still gets you $5k and 5 years. You can get licensed, but the cost is impractical unless you are running a sizeable distillery.