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That's not really how a blockchain works. A blockchain is more of a historical record, sort of like a banking ledger. It purely records the activities that took place in the past while acting as a shared ledger that everyone has a copy of and can validate the accuracy of through the use of a cryptographic algorithm. This in turn creates security through consensus of the math proofs involved. It's sort of like a recording tape without the ability to rewind and overwrite things because it would ruin the integrity of the original recording.

Cloning parts of old blocks and replaying them doesn't really work because you can't just cherry pick what's in them when you replay them. You wouldn't want to just replay the whole block because most of the data would be useless, stale data that was just being replayed and reproofed for nothing while wasting valuable computational resources. You either have to create a whole new block that consists of purely good data , or start a whole separate fork off the original chain which historically has been disastrous for some currencies. (And very thoughtfully was covered in the open source licence agreement of STEEM.)

I'm not sure if you're familiar with the Ethereum Project and the whole Ethereum, vs. Ethereum Classic ordeal but I'd give it a quick read through to see what I mean as to why "replay attacks" are a very real threat in those kind of situations. In summary the Ethereum Foundation decided to roll back their blockchain to reclaim a multi million dollar loss because of an exploited bug in their code. While some supported the rollback as a form of bailout, others did not and that's when the situation grew even more dicey.

Total chaos ensued because some people continued along the new Ethereum fork and some marched on producing work on the old Classic fork. Blocks with duplicate ID numbers were being generated and both proven to be correct which further helped rain down the chaos when you're talking about a blockchain that stores people's accounting records and wallet addresses.

It's actually a really great story and will be remembered forever in history as one of the greatest crypto blunders of all time. I was going to try and summarize everything but it's simply too complicated of a topic to cover in a one page reply.