It is completely legal to make changes and reference the author’s original design as your source of inspiration and label it as your design.
Derivative works of copyrighted materials are also a violation. It’s hard to quantify what degree of change is needed to not be derivative. Some have argued that all designs are derivative. Others hold (perhaps facetiously) that all designs are derivatives of designs so old they aren’t copyrighted. Probably the only thing that saves us is that the settlement isn’t worth the cost of litigation 🙂