In an earlier question, I was misusing Google translate to try to get the spelling of a word, and I was pointed to http://translit.cc which would directly furnish spelling instead of trying to guess a preimage in English that would translate in Russian to Владыка.
Now I am wondering about transliteration from modern Russian to Church Slavonic, or if that's not available transliteration from modern English to Slavonic. The LMGTFY-grade answer I'd anticipate is to simply change like letters for like, as a transliteration between alphabets rather than a transliteration between completely separate languages. However, I'd like to avoid beginner's mistakes.
Is there a tool comparable to http://translit.cc, or should I just replace modern letters with ancient precursors and trust the naive approach?
In the hopes of allowing this question to be reopened, I am adding what I put as a comment:
In my experience, English speakers who do not know Russian refer to the language of traditional Russian worship as "Slavonic" / "Old Slavonic" / "Church Slavonic." Native Russian speakers invariably, in my experience, say "Russian." I've read the Bible three times through in modern Russian and I'm chewing my way through the Slavonic, and the language is identifiably Russian. The linguistic distance between the Slavonic Bible on the one hand and a modern Russian translation on the other is about twice the distance between the KJV and the NIV, and the KJV is universally called English.
I know several Russian Orthodox, and all of them to my knowledge would place a question about old and new forms of Russian alphabet under the heading of the Russian language.
For further evidence, you might see a Russian video of the tale of Peter and Fevronia. After an initial animation showing an acronym in modern Russian letters, all the Russian that appears on the screen (the title of the video, a banner, people's names, etc.) are deliberately written in the Slavonic alphabet. The language of the video is modern Russian (plus English subtitles), but in Russian and in general there are times where it makes sense to Russians to write Russian content in the Slavonic alphabet.