Hoard books (no novels) and candles. Do what Krones did - use natural field medicine. At my age, I would consult with and fire up others to find a way out of those dark ages until they come to torture and kill me. Then I would be ready for a fatal dose of hemlock and know I have lived a life worth living.
I’d use all of the knowledge I have of theism, become a priest or something high up in the order of whatever, and as any good double agent would do, ensure the downfall and internal rot of the system, making sure that the intellectual property seized by the machine was systematically released in order to ensure the safety of the future.
Also, troll the $&@# out of the inevitable militant wings. I’d have them hunting the Scientologist “witches”. Lol
I wouldn't be anything other than what I am but if I had to chose a religion I would be ok with being a wiccan. When I was one I had JW's running and I did nothing but tell them they were just in time to help me finish a spell. Not that I actually had a spell going but they didn't know that. They had a booklet that said wiccans were satan worshipers or something.
Since literature wasn't allowed during the dark ages, I would bury my books in a special tomb with lessons on how to read our alphabet that hopefully is found by a future race. I'm a bibliophile, so I have many, many books. Bibliophile. Does the word sound dirty to anyone else, too?
Are you sure that the Dark Ages ever really left? Even the so-called Age of Enlightenment was for intellectuals only, and most of them did not discard their religious beliefs. Even those who did were usually very cirumspect about it for fear of their own lives.