I have successfully been able to swap licenses by first installing a retail version. At the end of this article you will also find a video tutorial on how to do all of this if you do not want to read all of the below.

PRETEXT

Windows 8 OEM machines no longer include a COA sticker or label at the bottom of your laptop with your serial number. If you need to re-install your Windows and your hard drive's recovery cannot be accessed or you forget to create recovery discs - it's a difficult process.

Here are the reasons people want to clean install Windows 8.1:

1. Some people believe a clean install is better than an upgrade from Windows 8

2. People forget to do a recovery disc backup and their hard drive's recovery doesn't work. This could be for a variety of reasons (mine was a new SSD installation, while others have reported wiping their drives or recovery partitions becoming inactive or corrupt)

3. Guaranteed removal of bloatware—even if you did obtain recovery discs, people don't like all the added on applications that OEMs supply with their machines.

4. Saving the $$$ involved in obtaining recovery discs from the manufacturer (such as Toshiba who thought it was ok to charge me $68 US to ship me recovery discs—with bloatware)

Here is the process

First, find yourself a retail copy of Windows 8.1 ISO. Get the version that corresponds with what came with your laptop (e.g. Professional 64bit). You can download from My Digital Life forums or even find one as a torrent or download directly from Microsoft if you happen to also have a valid retail serial number or dev account. (Remember, downloading a Microsoft ISO is NOT illegal as long as you are installing it with a legal license)

I recommend to check the SHA-1 hash to make sure the ISO files are original if downloading from torrents, else you may end up with a tampered OS with backdoors which will be nearly impossible to remove (implementing backdoors on a OS install disc allows to bypass any security measure of the OS and thus make them completely undetectable). You can check the official SHA-1 hashes directly from Microsoft's MSDN website, then just click on Details on the entry that corresponds to the ISO you downloaded to show the hash.

Next, install the ISO by burning it to a DVD and booting from the DVD. You may have to change your BIOS settings to allow booting from DVD as the first boot device.

Install Windows 8.1 Retail with a generic key. Microsoft has now released LEGAL generic keys used for the sole purpose of installing Windows 8.1 as an INACTIVATED copy.

Generic keys can be found by simply googling:

windows 8.1 [version] [32 or 64 bit] generic key

Finally, once the Windows installation finishes, open up an elevated command prompt. To do this right click on the Windows button and click Command Prompt (Admin).

In the window type: slmgr /upk

This will uninstall the product key (which is generic and inactivated anyway).

Once this is done, use a program like RW Everything to extract the key that is embedded in the bios of your OEM machine. Once you open it, click on the ACPI button then click the MSDM tab. Your key will appear at the end of the data window as the value for the key "Data".

Open an elevated command prompt again and type: slui 3

This will open up a GUI request for your product key. Paste the key from RW Everything.

That's it, you're all done.

You will notice you are fully activated and all of your Windows updates will work.

I have also made a simple tutorial video that explains how to do it all for those that want a more visual demonstration.

The Windows 10 upgrade stores your machine ID on Microsofts servers. This means that if you decide to do a clean install at a later point in time, you do not have to type in any product key and that you can just skip it during installation. After installing it will then activate itself (This may take a while.. Took a few hours and some restarts for me).

I actually decided to test this yesterday when installing, so when I was finished upgrading to Windows 10 I extracted the new product key from my registry and then I tried to do a clean install using that key. Sadly the Windows 10 installer doesn't recognize that key as valid.

In short: It doesn't look like there's any "magic" way to circumvent the upgrade method on the first install, since you need to get your machine ID up on Microsofts servers to be able to activate your Windows 10 installation.

Are you sure you need to get all the updates for Windows 7 first? On my laptop I was able to upgrade to Windows 10 directly on top of a fresh Windows 8 install.

Update: You could try to contact Microsofts support. Apparently a few people have had success getting them to upgrade your existing key to a Windows 10 key - Haven't tried it myself though so I can't confirm it.