You're not giving us enough information. Here's the best I can do with what you've provided:
"The Chawush moreover, is the other's superior in rank and roguery" = The Chawush has more authority and fewer scruples.
"Yet not of such rank" = Not powerful enough.
"That his mission to the Signory was any better than one of the covert insults dear to the Asian diplomatist" = To do more than just annoy the Signory, as an Asian diplomat in the story likes to do.
Student or Learner