I don't know of any.
--edit: Actually after googling "Roma Aeterna" i noticed I appear to have misremembered the name of the original alt-hist scenario I mentioned. "Roma Aeterna" appears to be the title of a nonsensical alt-hist novel by Robert Silverberg (various nonsensical PODs spun together to make the Roman empire survive to the present day without any stagnation). The EU3/4 mod attempt was for this novel, not the scenario I had in mind.
The "Roma Aeterna" alt-hist scenario I had in mind, was by a different author and not published in book form. I remember stumbling over it while browsing the website of another alt-hist scenario (dealing with the popular what if the Nazis won premise)
http://valtakunta.eu/ . I don't know the name of the author unfortunately, and this website seems to have been changed so that you can't actually view most of the content. And it's no longer accessible in english but only in Finnish, perplexingly.
The Rome scenario was AFAIK also by the same author, but as a bit of a side project. The premise was basically, that Christianity for some reason got suppressed by a more vigorous Roman Empire and instead Neoplatonism more or less took its place (as much as a philosophy can take the place of a religion, that is.) The scenario itself then dealt with the course of history in Europe as well as in China from roughly 60AD to the 16th century (by our reckoning). It was a thinly veiled swapping-of-roles between the European and Chinese civilizations - Europe under the Romans embraced Neoplatonism in the way the Chinese had embraced Confucianism historically, and fought organized Christianity in the same way the Chinese had fought organized Buddhism in the middle ages. Basically destroyed it as a political force. Europe/Rome then basically has a couple of dynasty changes but remains culturally Roman, and ends up in a complacent stagnation in the 17th century. No/little world exploration etc. Meanwhile China for some reason develops not as a united empire but as several empires (a little along 3 kingdoms lines) from the 3rd century to the 17th, and consequently (according to the scenario) embraces a more diverse, more outward-looking, and more adventurous course which of course leads to Chinese discovery of the Americas.
The scenario isn't really as fleshed out as it would need to be to form the basis of, say, a EU4 mod. It appeared more as a speculative philosophical exercise.