User blog comment:RemosPendragon/Questions to ask/@comment-33731050-20150226092833

Adeptus Mechanicus and Cult Mechanicus are interchangerble, 'adeptus' is the orginization and 'cult' is the religion. But they are really the same thing.

Only the priesthood are called 'tech-priest', but there are defferent ranks within that. Tech-Adept and so on. They do have specialities, or at least they did in the 30k era. In 'Mechanicum' there were several disciplines of the Tech Cult, but I'm not sure if they still exist in 40k, though I'm guessing that they do.

I have no clue about the Imperial Guard though.