[NoeJeko]

If he rebuilt the skin from the ground up, then he can legally remove the copyright notice as this is considered a "derivative work" under US Copyright law.

Originally Posted by 17 U.S.C. ? 101

A “derivative work” is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications which, as a whole, represent an original work of authorship, is a “derivative work”.

As long as it's an "original work of authorship", even if it's based upon an existing work, it's still legal. Us courts have upheld this multiple times:

Sega Enterprises, Ltd. v. Accolade, Inc.

Lewis Galoob Toys, Inc. v. Nintendo of America, Inc.

While the "derivative work" law on software is not completely clear, this does not fall under the realm of software since it is a design in question.

I'm not saying either side is right or wrong and only a code analysis could truly prove if the OP did indeed infringe upon the rights of the original author, but I had to clarify some misconceptions I've seen here about copyright law. As a coder, if someone saw a mod that I've written and completely designed their own - with similar functionality - from the ground up utilizing none of my original code then they are not in violation of anyt copyright I may claim over my work (unless such work is protected by a patent - and nothing here is).

My information is cited from Wikipedia, http://en.wikipedia.org/wiki/Derivative_work