[csomar]

Not really. you are talking about an attack.

You'll need 100%, because if a single miner decided to include the transaction, then it is in!

[maaku]

You need only a cabal of >50% of the miners to agree to not build on any block that includes such a transaction.

[jsprogrammer]

An attack and a new protocol are the same thing.

If a single miner includes the transaction, a majority can just bypass that sole miner.

You do need 100% of something, but that something is just >50% of the miners.

[bduerst]

Only if that miner is successful for a block. Until then the blocked transaction stays in limbo.