Originally Posted by Happy Jack
It's entirely a case-by-case thing. It's dependent on the stories and characters you're working with.
Originally Posted by Edguy
Pretty simple; "will changing this element make it a better movie and/or a more viable franchise?"
Yes? Do it.
At this stage in the game, there's enough examples of any scenario to put this question to rest.
The only thing I'll add is that film makers should quite simply use whatever works while still keeping the character identifiable. e.g. you wouldn't have Superman running around at night in a black trench coat killing vampires, no matter how good the script may be.
If, for whatever reason, the character just can't remain identifiable at all, then the movie is better off not being made. That's admittedly a bit of a stretch, as I think most comic characters can make the transition to the silver screen, but some require more tweaking than others.