I’ve been beating my head against this problem, and just found a solution, so am sharing here in case anyone else finds themselves trying to keep certain text from getting auto-transliterated. This solution is both counter-intuitive and shady.
In a nutshell:
If you have non-vernacular text that should not be auto-transliterated by an encoding converter but rather be published in its original encoding, wrap it in a custom character style, and give that custom style the nonpublishable property.
Yes, the nonpublishable property rather than nonvernacular, as would have seemed fitting. The nonvernacular property does not actually affect what gets transliterated, and the nonpublishable property does not currently affect what gets published, at least not by Publishing Assistant.
Detailed background:
I’m about to typeset an auto-transliterated project. The project contains certain words in the national language. These can be found in glossary entries, in introductory material, and in footnotes, and are tagged within \znp …\znp* markers, which I’d defined in custom.sty as a nonvernacular, publishable character style, because that’s what it was.
In the primary/source project, the vernacular text and the national language text are both in the same writing system. In the auto-transliterated project, the vernacular text should be converted into a traditional script used only for this language, but the text in the national language should come through as it was in its original script. (The traditional script cannot represent the retroflex sounds found in the national language, and it would be weird to see the national language in the vernacular language’s traditional script in any case.)
But marking such text as nonvernacular had no effect on keeping it from being transliterated.
Nor could the TECkit map be told to ignore text enclosed in \znp …\znp* markers, because the markers themselves are not passed into the map for processing. (Presumably they used to, because the Paratext Help documentation still says, “Be sure the TECkit.map file you use preserves the USFM markers so they will not be converted.”)
The tricky solution was to change the publishable property to nonpublishable. This did not prevent Publishing Assistant from publishing it.
I don’t know whether that will mess things up with other output paths (SAB / Print Draft / PtxPrint / YouVersion via DBL), whether currently or in the future they will quietly drop unpublishable text, so that is definitely a concern with this workaround.
Other than nonpublishable exempting text from auto-transliteration, it’s not clear to me what other effects either of these properties might have. Is there documentation somewhere that explains this?