>>> How can we tell that a 'charlatan of old' didn't manage to re-write a few injunctions from the HOLY scriptures of ancient times?
Short Answer: They did. The dead sea scrolls are a prime example. HOW do we know ? Simple from hundreds, even thousands of other copies that agree with each other and don't have the 'charlatan changes'.
Being a scribe in olden days was considered a grave and honourable undertaking.

Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...