I am making a new NPC and am currently assigning said NPC topics. Moreover, this NPC happens to be aligned with the Fighters' Guild ranking at apprentice. I've added a topic response exclusive to this NPC's id. Other than excluding the NPC from the default response, how could I make the intended topic response display? Are responses dependant on PC rank specific to that rank or are they included with bigger ranks as well?

I'm not sure what you mean.. be a little more specific. What I can recommend is putting your topic above the offending topic.

I think this would sort out the problem the OP is talking about - basically, if you assign a topic specifically to one NPC, the relative rank or guild won't matter, as it will only come up for that one NPC. But their specific response has to be above the other possible responses, otherwise the NPC will respond with the more general dialogue.

Dialog is "read" from the very top down and the first response that all of the filters fit is displayed. Try moving your topic above the one that's being displayed ingame and that should fix it. If it's already above that response, we'll need a screenshot of the offending lines in the CS.

I can't seem to wrap my mind around randomized greetings and how to prevent characters from using the default Morrowind ones.