I wouldn't claim to be an artist, but I would claim to be a lawyer (within my jurisdiction, of course). As far as U.S. copyright law is concerned, a modification of an original mesh, no matter how extensive, would still be a derivative work and thus infringe on the copyright of the creator. Of course, as a practical matter, it could be possible to so drastically alter a mesh that the creator might never suspect, let alone be able to prove the infringement. To give an extreme example, if someone took the P4 nude woman and modified her into a coffee table, deleting thousands of vertices in the process. Moreover, in such an extreme case, despite the myth of percentages, there is a "de minimus" rule that might be invoked as a defense. But the post above giving the hands example is correct; the hands were spotted right away. A complex mesh like a human figure is likely to have a number of unique points and relationships, including flaws in design, that are likely to be spotted in a similar derivative work.