Is there any generally useful magic that can be done if all it could do was violate the Third Law of Thermodynamics?
The Third Law of Thermodynamics just seems to relate to absolute zero? And it says that:
It is impossible for any process, no matter how idealized, to reduce the entropy of a system to its absolute-zero value in a finite number of operations.
Physically, the Nernst–Simon statement implies that it is impossible for any procedure to bring a system to the absolute zero of temperature in a finite number of steps.