You do realize though that changing just 1 bit can change the entire hash? What's to prevent people from appending a random bit or two, and getting an entirely new, unblocked, hash?
I think blocking a hash can already be a victory, since it basically makes all the metadata that was associated with the hash useless and forces reseeding under a new hash and publicizing that hash. As long as you make it inconvenient enough, very few people will bother, which is the best the copyright holders can hope for.
Reseeding might be pretty easy though in IPFS since there is a block layer below the object layer, and I guess you can't really block block-hashes.