Nope, 51% attack is a soft fork, not hard fork.
My impression is that even if it worked it would effectively be a hard fork, and the existing nodes would refuse to recognize transactions as long as they have the existing software.
But I could very well be wrong, because I'm still pretty fuzzy on how all of this works, but it has stuck with me that nostr:nprofile1qyv8wumn8ghj7urjv4kkjatd9ec8y6tdv9kzumn9wsq3vamnwvaz7tmjv4kxz7fwwpexjmtpdshxuet5qyvhwumn8ghj7um9dejxjapwdehhxenvv9ex2tnrdaksqgqyey2a4mlw8qchlfe5g39vacus4qnflevppv3yre0xm56rm7lveyr9lldz recommends not upgrading nodes with new software immediately.
Discussion
oooh - thank you! I hope the original poster sees your note