"What happens if we cooled the core to the point that it became solid? " That would be very, very bad, but if you look at the numbers, like others pointed out

"What happens if we cooled the core to the point that it became solid? " That would be very, very bad, but if you look at the numbers, like others pointed out - this is not an issue with our current tech. I would be more worried about earthquakes and co. because deep plate tectonic is not understood well. And when you cool one area significantly, that creates tension in the rock, because of the heat difference to other hotter areas.