So, I installed Windows 8 Pro on a custom built PC for a customer. He forgot to buy Windows, I told him no sweat, I will install Windows with a generic key, and after he buys Windows, I can install the new key and activate for him. Problem is, I installed Windows 8 Pro with generic retail key ending in C9WKB, and what he bought was an OEM System builder License. So, I cannot activate Windows for him. Can I change the install channel from Retail to OEM, and install his key? I sent him to the store to get a Retail version in case not. Stores have a pretty strict policy against returning opened software, so I am trying to save him $200. From what I know, I can change the install channel on the install cd (ei.cfg), but that would mean I would have to do a clean installation, and the customer has already spend an entire day transferring his files and programs to the new computer. Thanks for any help!