Downgrade Huawei P8 Marshmallow to Lollipop Firmware

Transition Firmware Details:

• Device: Huawei P8
• Model: GRA-UL00
• Android: v6.0 Marshmallow To v5.0 Lollipop
• Build: GRA-UL00C900B300
• Status: Official
• Release Date: 8.02.2016
• Region: Europe
• Country: Russia
• File Name: RollbackMiddlePackage_GRA-UL00C900B300_Android 6.0 to Android 5.1.zip

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How to Downgrade:
Unzip the transition package on your computer.
Transfer the dload folder to the external microSD card.
Safely disconnect the USB cable from the PC.
Dial *#*#2846579#*#* to open Project Menu.
In the menu, go to Software Upgrade > SDCard Upgrade > ‘OK’.
Once the device reboots after installing the transition firmware, make sure the Build number says ‘GRA-UL00C900B300’.

Now you can install whatever Lollipop build (for the UL00 variant, of course) you want – like B132 using the exact same procedure.