IANAL, but from my understanding, the primary law used to prosecute hacking is the CFAA's broad "without authorization" and "exceeding authorized access" clauses.

That said, authorization implies an entity with ownership rights granting some kind of limited license to others to interact with the owner's property.

For a permissionless decentralized network with no owner, where the attack is against the consensus of which chain is valid, I'd have a hard time arguing that "authorization" as a concept is even applicable or relevant.

As wmf suggested, market manipulation laws may still apply, but I'm not sure traditional CFAA "without authorization" / "exceeding authorized access" hacking charges could apply, though I'd be willing to bet a prosecutor could make a case for wire fraud - a scheme to defraud using interstate communications.