The company I work for used to have 8 computers running Windows XP. All computers had pirated versions of the OS (don't ask me how and why). We now bought 8 new licences with VL key. My question is this: From the legal point of view, do I need to reinstall Windows XP on all 8 computers, or can I take the short route and just change the product key in the registry?

Thank you for your answers.