Can anyone who knows the Slavonic language speak to how well the compositions fit the Slavonic texts in general? In other words, to what degree does the accentuation of the text match the melodic accentuation of the music?
For me the correspondence between melody and text is good. The accentuation is not matched as strictly as in the Greek compositions, but I think this is normal because Slavonic is not live but more or less artificial language. The official Slavonic accentuation doesn't follow the Russian, nor Bulgarian and even less the Serbian accentuation so the wrong accents do not always sound wrong.
Has adherence to the formulaic rules improved, deteriorated, or remained constant from the older editions to the newer editions?
I don't think the composers of 19th century knew about any formulaic rules. They lived with this music and they used it the same way we can speak our languages even if we don't know all grammar rules.
For me personally, some of the compositions for the Liturgy are too far from what I feel the tradition is. But I think this is a problem for Greek too.
From what I know, the best compositions are those in the books of Angel Sevlievetc. His Voskresnik (Anastasimatarion, 1859) was examined and approved by the chanters of the great church in Constantinople and it carried the official seal of the Patriarchy. These books are not available in the net but his compositions were reprinted in the books of Manasia Pop Teodorov (available from the 'Slavonic Psaltic Resources' on analogion) and they are de facto standard today.
Another question I had was: Are the prosomia in these books translated according to the meter of the original Greek (either loosely or strictly)?
I think no change in the established liturgical text for the sake of the melody would be approved for use in the Church. I am not sure the Slavonic language is a good example for the modern translators because it is a linguistic peculiarity. The Slavonic translations follow the Greek original word by word. In order to permit this, St. Cyril and Methodius invented Slavonic correspondences to all the complex syntactic constructions of the Ancient Greek language. I suppose at that time this wasn't a strange thing to do because if the Greek people in their everyday language didn't use the ancient syntactic constructions and yet they used them in their literary language then why shouldn't the Slavic people use the same syntactic constructions in their literary language even if their spoken language is simpler. In several cases the Greek-Slavonic correspondence is not only on syntactic but even on morphological level, for example καὶ->и, γὰρ->бо, καὶ γὰρ->ибо.
Word-by-word correspondence means no meter is possible.
Is anyone able to make available scanned copies of the compositions and musical books of Kalistrat Zografski? He wrote wonderful compositions is
psaltic notation and should be better known.
There are scanned copies of these books but they are not very useful because there are two pages per tiff-image and these pages are not adjacent (for example page 60 is combined with page 41). Go to
http://www.ierodiakonjustin.info/. Then click on "Изтегляния" (on the left side) and then on "Невми". There you will find several Slavonic musical documents. Go to "1. Ежедневно и празнично богослужение" and then on page 2. The books you are asking for are these: "Зографска Вечерня", "Зографска Литургия" and "Зографска Утрена".