The manuscript culture and therefore proper scribal monks didn’t crop up until around the tenth century.1 It would be impossible for medieval monks to change all of the existing copies of the New Testament. By the beginning of the medieval period there were at least 800 copies of the New Testament text. We know this because pieces of these manuscripts are still available today; some in their entirety. Experts have estimated that Of all the works of pagan Greek literature perhaps only one percent has survived until today.2 If this number is also accurate for Early Christian Manuscripts, it means that there could have been tens of thousands of copies of the New Testament in circulation by the beginning of the medieval period.
In order for medieval monks to change the story of Christianity, they would have to track down all of the tens of thousands of manuscripts that existed across three continents, in four languages. They would have had to have perfect forgery penmanship in Greek, Latin, Syriac, and Coptic. Each codex of scripture was highly revered and guarded as a priceless treasures, so not getting caught doing this would be quite impressive.
They then would have to learn to lie in all those languages in order to fool the audience. An audience, by the way, that was already familiar with the stories contained in the manuscripts. They would then need to have all those who noticed the changes silenced.
The claim that medieval monks could have changed the biblical story somewhere in the middle ages is impossible. Today archaeologists have recovered around 25,000 manuscripts or fragments of the entire Bible. It’s a ridiculous conspiracy theory when you consider that these thousands of surviving manuscripts are near identical. As far as conspiracy theories go, this one is an extravagant one. The much more elegant explanation is that those manuscripts are unaltered.
1 Voigts, LE. “Anglo-Saxon Plant Remedies and the Anglo-Saxons.” Isis (1979): pp. 260-268.
2 Blum, Rudolf. Kallimachos : The Alexandrian Library and the Origins of Bibliography. Vol. Wisconsin studies in classics. Madison, Wis.: University of Wisconsin Press, 1991.p. 8