A well know XDA Developer and Software Hacker, HeathCliff, has made it possible to unlock Windows Lumia phones for Root Access and run Custom ROMs. This he made possible by developing a tool called "Windows Phone Internals".

List of what Windows Phone Internals can do include:
Unlocking the bootloader of specific Lumia Windows phone models, and then enabling root access.
Enables you to install Custom ROMs.
Enables you to load custom apps with higher privileges and without sandboxing in Windows phone OS.
Enables you to create a Backup images of your phone and access file system in Mass storage mode.
The Lumia Windows phones supported by Windows Phone Internal are;
Lumia 1320
Lumia 1020
Lumia 920
Lumia 820
Lumia 720
Lumia 620, 625
Lumia 520, 521 and 525

Download the file and also see instructional YouTube videos below.

http://hotfixtech..com/2015/11/how-to-root-your-windows-phone-and.html?m=1

Noted

This is getting interesting.