Pardon my ignorance, but if the attacker has stable 51%, even if we all change our clients to support the new suggested rules, all our blocks will be still rejected, won't they?
No, because the attack blocks would be invalid, and thus not in competition for the regular blocks,
at least with the nodes that have adopted the new rules.
But, if such nodes will be less than half of network, the prevailing (so considered true) blockchain will skip our blocks. As a result, the blockchain will be hard forked with all our "sane" blocks scheduled soon or less to be completely overwritten.
I still suppose that the rules are the same for all, regardless for bad or good boys. There are just majority or minority boys left. (No pun intended).