Prevent Windows 10 installer from using the preinstalled serial key without disabling UEFI

My laptop (a Lenovo Flex 2 15) came preinstalled with Windows 8 Standard (with the serial key preinstalled into the BIOS), and I've since installed an SSD (a Samsung Evo 840 120GB) & upgraded to Windows 10.

When the laptop still had its hard drive, I upgraded it to Professional so I could use the resources provided by the domain on my homeserver; because of this, I can only use the Professional editions of Windows (Home can't join domains).

I bought Windows 10 Professional & completed a fresh-install (complete reinstallation) of Windows, only that it installed Windows 10 Home instead of Professional. I'm guessing this is due to the Windows 8 Standard Edition serial key preinstalled in the BIOS.

I then downloaded an All-In-One ISO image of Windows 10 from MSDN (of which I have limited access to), transferred the installer onto a USB stick, & reinstalled (a clean install again). However it's still installing Windows 10 Home.

If I try to install using the AIO image from within Windows, the installer does not present me with a list of options for the edition I want to install; instead, it assumes that I want to install Home Edition:

I am able to get Windows 10 Professional to install if I disable UEFI & use Legacy instead, but I feel that this is stepping around the issue rather than resolving it.

Is it possible to have the Windows 10 installer ignore any serial keys preinstalled in the BIOS/UEFI? If so, how? If not, is using Legacy mode really the only way around this?

Answer

First of all, make sure you have a regular (single-architecture) Windows ISO. It seems you already have that covered.

Then, try this method:

1. Create a Setup USB drive


2. 
   

   Create a file named PID.txt in the Sources directory, with the following contents:

   
   

   [PID]
   Value=YOURK-EYGOE-SHERE-XXXXX-XXXXX
   



3. 
   

   Boot from this USB drive