I noticed a bit of changing between Axel. Axel had a smaller, cute-teenager-kind of face... though, in KHII, he matured. I even sensed a bit of a height difference.
If you look at their line up (I can't find it)
They may have made a new Axel model, but I sincerely doubt it. Take a look at Sora and Riku--they're the same age as in KH1, but there were some significant changes to the quality of model. If they changed Axel, it would have been much more significant.
The only thing I noticed about him was that his hair seemed to stick out more in Re:CoM, but I think that's because he was often in positions that made that happen (for example, when he turns his head to talk to Larxene right before she puts her fingers to his lips, his hair is all of a sudden sticking out almost horizontally to avoid clipping through his shoulder).