See reply to mk. Not entirely sure what a "ledger" has to do with a system that prevents "memory holes" ala "1984". git pull from 'authority x' and mod, commit, and publish on your own (or an alternative) server. What is the issue?
The Blockchain uses cryptography and its decentralized nature means that one would have to not only crack the crypto but corrupt all copies of the blockchain to successfully change its past records. How does GIT prevent past records from being modified?
Well, Git uses SHA-1. It is a cryptographic hash, but of course vulnerable to collisions and already a bit deprecated. But a Git like system with a more robust hash (SHA-3, if you will) addresses that. (That paper that was gibberish explains it.) [p.s. Same with git re. 'copies'. If someone somehow manages to hack the SHA-1 sig for a commit on github for repo x, all the extant clones of the repo still maintain the original records and can challenge it.]