Is it true that the difficulty can be changed with a patch accepted by 50% of nodes? Doesn't this mean that an attacker only needs to set up a bunch of nodes and not actually have a majority of cpu power? How hard would it be to do an attack like that? What does it take to have a node? A 2880 bps modem and a Pentium 386? Can a computer hold multiple nodes?
I don't think so. I think that if you created a block with lower difficulty than what I think is the current difficulty, I wouldn't accept it. That means I wouldn't accept any coins that originated in a block with this lower difficulty. This would effectively split the network in two.