It's easy to add a special party to a block-chain which does have the power to make arbitrary transactions. Can that be abused? Yes. But all such abuse will be

It's easy to add a special party to a block-chain which does have the power to make arbitrary transactions. Can that be abused? Yes. But all such abuse will be evident in the public record, and then the usual legal system can easily get involved -- which it already did anyway, if you're doing a proper IPO just with stocks tracked on a "block chain".