When Microsoft officially released Windows 10 Mobile as an upgrade for Windows Phone 8.1, it was a great day for many users. However, at the same time, many users got disappointed to learn that many older phones, including the Lumia 920, 925, and 1020 will not be upgradeable to the new version and they will no longer receive previews of any kind.
However, if you still really want to upgrade your Windows Phone 8.1 handset to the latest Redstone preview builds, you can unlock your phone and replace a few registry keys to pretend your phone is a supported model giving unrestricted access to download and install the latest releases of Windows 10 Mobile.
In this guide, which was originally posted on the XDA Developers forums, will help you with the instructions to enable your unsupported Windows Phone 8.1 handset to Windows 10 Mobile Insider Preview.
Install Windows 10 Mobile on unsupported Windows Phone 8.1 handset
Upgrade your Windows Phone 8.1 handset to the latest supported Insider preview build using the Windows Insider app.
Open the Settings app.
Navigate Update & security > For Developers and tap Developer mode.
Download the Windows Phone SDK tools 8.0 lite from ZippyShare.
Double-click the install.bat and click Yes on every prompt to install the SDK.
Browse the following path and launch XAP Deployment.exe:
C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v8.0\Tools\XAP Deployment
Download and deploy @vcfan Lumia registry editor vcReg_1.5 using the XAP Deployment.
On your phone, open vcreg, tap (…), and select templates.
Check the options Live interp/Capability Unlock and Restore NDTKsvc, and click Apply.
Download and deploy Custom PFD 6 using the same XAP Deployment.exe tool. If deployment is successful, jump to step 15.
If you’re unable to deploy, then download the Windows Phone SDK tools 8.1 light from here.
Extract its content, double-click InstallWP81SDToolsLite.bat, and accept prompts.
Browse the following path and launch AppDeploy.exe:
C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v8.1\Tools\AppDeploy
Deploy the Custom PFD 6 package to your phone.
On your phone, open Custom PFD 6.
Navigate to HKLM > System > Platform > DeviceTargetInfo, take a screenshot (press and hold the Power and Volume Up buttons simultaneously) of the original values and move to SDcard. You’ll be able to restore the value at any time.
Change PhoneManufacturer to MicrosoftMDG.
Change PhoneManufacturerModelName to RM-1085_11302 (for Single SIM devices) — and for all dual sim devices change the value to RM-1116_11258.
Change PhoneModelName to Lumia 950 XL (single sim) or Lumia 950 XL Dual SIM (for dual sim).
Change PhoneHardwareVariant to RM-1085.
Make sure your phone is fully charged and connected to a charger.
Download Windows 10 Mobile Upgrade Advisor from the Store and try to install the new version of the operating system.
The instructions on this guide should work to most unsupported Windows Phone 8.1 handsets to upgrade to any Windows 10 Mobile Insider Preview builds — including build 14322.
However, I would highly encourage you to visit the XDA Developers forum and carefully read all the instructions, risks, and comments from other users that may have tried these steps before proceeding, because it’s not guarantee that will work for everyone equally. In addition, there has been reports from users complaining bootloop problems installing Windows 10 Mobile build 14322, and the forum entry also warns of different bugs that you may come across installing Windows 10 Mobile on your unsupported phone.
Source XDA Developers