AHH! The frozen king crab you buy at the market IS COOKED.
I worked for a seafood processing/packaging plant in AK for three years, and a good portion of our business was mail order king crab. It was absolutely, always, 100% cooked as soon as it came off the boats. The "story" about crab becoming poisonous once it dies (if not cooked) is absolutely true.
When we shipped ours it was cooked immediately, flash frozen, and shipped overnight with gel ice packs. Dry ice should work fine too as long as you really protect the crab from direct contact.
The best way to warm it back up once frozen is to allow it to thaw in the fridge overnight, then quickly steam it in a large pot, just until warm. Or just eat it cold.
Fun story about dead crab- we once had a fisherman offload an entire boat of dead king crab on a Friday afternoon. The plant manager let it sit over the weekend and by Monday morning the smell coming out of the building was so pungent we were all sick trying to work in the front office. I had to get rid of all of the clothes I wore that first week. Mmm. One crab had died and poisoned the entire load. Nasty and awful.