okay, i haven't been doing serious climatology for more than a year, but with just the little i know the ideas presented here don't have merit.
it would require a great deal of energy to turbidly mix the ocean layer. the depth of the warmth is oceans is deepest in these currents, also... so redirecting water up from below in these areas wouldn't have much of an effect.
you would need a freaking enormous tunnel to do this and it would need to be powered to transport so much water (deep ocean water is heavier and more saline and naturally doesn't want to come up except in upwelling zones). you would need many of them to create an appreciable difference in the ssts across a large enough area to affect hurricane boundary conditions, or at least many to cool specific places to intercept storms (and they don't sound very mobile). small patches of cooling could actually help create gradients (i.e., the inward flow of nearby ocean heat to compensate) which have been noted as locations that hurricanes often rapidly intensity, and thereby be deterimental.
the idea that you can change a hurricane by altering local boundary conditions is a little bit nuts, but that tornado climatology could be affected is beyond silly. to get rid of the tornado-favorable conditions you'd need to shut off the low level heat transport over the continent from the gulf. that would screw up the climate over continental america, shorten growing seasons, allow arctic air intrusions more of the year. cooling the gulf that much, if possible, would cause DRAMATIC shifts in the climate, changes in vegetation, species, and have a cool the eastern u.s. back to late glacial type conditions. the tolerances of a lot of plant and animal species are much narrower than most people think. cooling the gulf that much would also likely alter the northward heat transport in the atlantic and screw europe up too. the law of unintended consequences would run amok.
but that's all hypothetical poo, because there isn't any way to modify ssts that much.
climate is a closed system. you push somewhere and it pushes back, or jumps stability modes. luckily the ability for humans to push isn't as great as some wish it was.
HF 1627z10december