There is nothing wrong with redrawing another artists piece and changing it to your style. One artist's version of a subject might be totally different from anothers. Look at all the variations of American Gothic, or the scream, or the mona lisa.
They arent copies so much as they are parodies or retellings of the same piece through the skill and style of a different artist. Its always cool to see how a different artist might have handled a certain image or idea.
In fact I had a contest that revolved around this very idea planned. Taking one artist's work and remaking it as your own. I scrapped it due to time issues but I might revive the idea one of these days.