http://www.copyright.gov/help/faq/Even if you change the product a lot, if it still recognizable as the original artists work, you are violating their copyright ( either registered or not).
" Your work is under copyright protection the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device."
"How much do I have to change in order to claim copyright in someone else's work?...;
Only the owner of copyright in a work has the right to prepare, or to authorize someone else to create, a new version of that work. Accordingly, you cannot claim copyright to another's work, no matter how much you change it, unless you have the owner's consent. "