One of the biggest things Satoshi did that made bitcoin and blockchain so powerful, is the hash of each block contains the hash of the previous block. So any attempts to go back and change a previous block would be denied because they will break every subsequent block not just the one you are trying to change. Mine is a very simple description, but hopefully you get the point. Theoretically it is possible to change the blockchain history if you have enough computing power. A state actor with lots of resources may be able to pull it off, but at enormous cost for relatively small benefit. So it is highly unlikely this will ever become an issue.