[rlpb]

> can rewrite the history arbitrarily

No, you cannot do that. Transactions would still need to be signed by the corresponding owners. All you could do is reorder (and thus invalidate) some transactions, drop some transactions, or add some that weren't originally included.

> Just dump everything into unusable addresses...

Nope; that's not possible. You wouldn't have the signatures to do that even with 51% hashing power.

[mjburgess]

You're right about the dumping; I was thinking more about the case where you controlled the protocol on the machines of a partitioned network (eg., so you release a new version of btc which uses exploitable crytography, etc.).

In the case of a mere 51% at scale, hijinks are still quite possible from replays, reorderings, etc.

I was more preoccupied by the case where the state's acting in its own borders with control over the network, major miners, most machines on the network -- at this point basically no gaurentees remain

[rlpb]

> the case where you controlled the protocol on the machines of a partitioned network (eg., so you release a new version of btc which uses exploitable crytography

Such a change would be treated as a "monopoly money" fork by those wanting to transact, and ignored. "No I don't want your fake money; send me real BTC or GTFO". This is why miners cannot arbitrarily change the protocol in their favour even today.