I am working on a blockchain learning project and i have a general question about block immutability. I know that when a block data is altered the chain becomes invalid am wondering what happens if I revert that change does the chain become valid again? see the following scenarios
Chain =Array('Block1'=>100,'Block2'=>200)
If I make a change eg
Chain[Block2]=300
Our chain is now invalid.
My question is if I reverted this change eg
Chain[Block2]=200
Is our chain now valid again or once a block is altered the chain permanently remains invalid