Avatar parts for cmc Guidelines

I sent this in an e-mail to you, but it seems like an important enough question that other people might want it:

What is the policy on modifying another person\'s avatar part?
e.g.: Create an alternate coloration of an existing part (say a red wizard\'s robe)
e.g.: Use an existing part as a basis for your own (say changing the wizard\'s hat into a witch\'s hat with a wide brim)