It's worth remembering that a 51% attack with different rules isn't sufficient to bring down bitcoin.  Miners are not the only bitcoin clients in the network.

The goal of miners is not to get transactions into a block chain, it's to get them into a block chain that bitcoin clients of intended receivers will accept.

Let's say I am a merchant, and you use your nefarious powers to subvert 99% of the mining power.  You still cannot force my client to accept your block with bad rules and therefore my client will never say "received 1000 coins from..." so you can't spend them even if you do get them in a chain.

51% attacks only work if the bitcoin rules that the non-miners look for are still obeyed.