It might be possible. It would certainly be terrifying.
I think what you should take from this essay is less a sense that
stopping the thermohaline circulation is an immediate danger, than that
the earth's environment is a vast and complex system, whose behavior we
are only barely beginning to understand.
The idea of humanity trying to take active control of the earth's
climate should be as reassuring as the idea of an 9-month old baby
turning off the auto-pilot of a 747 airliner to take direct control.
Of course, this may be exactly what we will have to do. If we mess up
the system enough, then we'll need to try to take countermeasures, as
best we can. If you've broken the auto-pilot, then you have to do the
best you can to fly the plane, whether you know how or not.
So there is nothing more important to do in the realm of climate than to
invest all we can in developing a better scientific understanding of the
earth's climate and ecosystem. We are far from knowing as much as we
need to know.
I'm no expert, but it seems like beaming heat down to specific spots
might (or might not) do some good in the short term, but would add to
global warming overall, and thus do more harm in the long term. Sounds
like a questionable idea to me.