So, I'm kind of guessing the answer is "no" already, but let's double check:

Let's say I realized after posting a manip/original image that I mis-arted a thing and would like to fix it. Is there actually any way for me to replace the original image with an updated one?

You can make your changes and upload the better version then flag the older one and a mod can take it down.

I guess. That seems rude to the people who've already bookmarked/favorited it, though.

Oh if you parent the old on with the new one then when the old one gets taken down the faves from the old one goes to the new one

Oh, that's cool. Alright, I'll do that once I'm done, then. Thanks!