There's a massive book in my university library, I think it's called "Movie Moods for All Occasions." It's got written-out classical excerpts arranged by mood, like chase scene or love scene. I suppose you study the book a while, learn a couple pieces for each mood, and then you're ready to accompany a silent film.
But as for the diminished-chord improvised accompaniment style, I've not seen any literature describing exactly what's going down with that, because it varies from performer to performer.