The answer to that question depends on the type of the change. In general, if simple modifications (for instance, turning a steal part to a part of aluminum) to the material do not really brings an advantage, they cannot be protected by a Utility Model or Patent since they are not inventive at all. On the other hand, if there are innovations (such as producing a lighter but more durable material by changing the material alloy) in the content of the used material, these kinds of inventions can only be protected with a patent because they are linked with chemistry and materials science.