Noooooooo.
A few years ago I was working on a comic when I was still pretty new to the whole thing. Once I got about 40 pages in, the beginning looked super bad, so I started re-drawing entire pages of the beginning. Which made the middle look bad. And then the new middle pages looked better than the newest pages. :u So I ended up with a comic with art styles all over the place. And I never finished it because of the constant re-drawing.
I do think it's ok to make a couple tweaks here and there, like what @joannekwan said about fixing a couple faces or panels. I've considered going back to the first chapter of my current comic and adding a little more detail to some of the panel backgrounds.
I agree with others in that it's nice to look back and see your progress. I like to see that in other peoples' comics, too. Just the other day I was comparing two similar panels from chapter 1 and 2 from my comic, and already I can see the improvement in the character art ~u~; but I will resist the urge to re-draw entire character drawings.
I think for anyone who's really worried about their style changing dramatically as they work on their comic, it's good to do a couple shorter series and find the style that works for you, instead of embarking on one long story and having dramatic stylistic shifts.