So, then how come that some guards say "Psst, I know who you are... "Hail Sithis" EVERY time I hear that, I want to kill that guard for knowing my secret! How stupid is that? They can say that, but on the other hand, they can't acknowledge that I'm the Harbinger or Arch Mage etc?
Now, I don't know if the unofficial Skyrim patch fixed that, but the guards in the towns now address me as "Thane" and ask me how things are. I also hear other acknowledgements, like OMG you wield the Star of Azura, how is this possible? They also address me as Harbinger etc. So, my actions did finally make an impact.
That was my BIGGEST gripe with Skyrim. The world felt like I was living in a vacuum, that no matter what I did, it really didn't matter and nobody cared...
Because those guards are part of the DB and serve as undercover guardsmen to be called when needed......................
Also, the guards DO call you harbinger, as for being arch-mage, no one really cares about the Collge, even the guards, they do know you joined the college, but what happens inside the college is largely a mystery to everyone.
As for the guards calling you thane, they already did that in the base game, but it was just super rare, in correcting some of the broken guard comments, and fixing the bugs that caused them to get stuck in loops of saying "what?" over and over again, it made previously rare dialogs more common.
But even after fixing it, ive heard guards call me thane maybe once in over 50 hours of gameplay.