Quote from this article https://blog.colony.io/why-a-post-hard-fork-ethereum-will-be-more-valuable-abc35bbf6e98#.2jfczxeho
Blockchains are not immutable. If they were, we wouldnt be having this discussion.
(Maybe I misunderstood what immutability of a blockchain means , so please correct me if wrong.)
Doesn't forking an existing blockchain actually create a "new" blockchain with similar past and different future?
The "old" one still exists with unchanged parameters/fundamentals and with enough support from miners it can be kept alive.
So there could be 2 different blockchains running in parallel. Ethereum and NewEthereum.
Can you change a blockchain without effectively creating a new one?
Wouldn't it be more appropriate to say "Peoples/miners choice (on which blockchain to support) is not immutable"?
Normally a chain that matters should only be forked if it is defunct or very close to being defunct - in such circumstances you get an easy consensus on forking it.
One shouldn't expect a consensus for a fork on a chain that isn't defunct.
That's the nature of the thing. The consensus-algo protects the chain from hostile takeovers. It's a feature, not a bug that the chain is hard to change. If no change is necessary, why would you change it?