[sodacat]

Changing a character's design, especially if it's short term (longer than a storyline, less than a year) can be difficult to do with the way comics are produced. When one storyline ends the writer or the artists could leave, and whoever replaces them is only going to be working off the standard models for those characters. They didn't sign on to write a character who's a werewolf, they signed up to write spider-man. That's not even getting into characters who make multiple appearances outside of their main series.

Basically unless it's a creator owned deal, or it's a small title that a single writer/artist pair can work on for a few years straight it's not going to happen.