[Huawei P9 Plus Guides, News, & Discussion] Tecalote:
Note: Oreo is only for Chinese models, if you want to rebrand your Phone from VIE-AL10c00 to VIE-L29c185 - you must first downgrade to Android 7.

This is required!

1) You can do this with the steps, which are written in Post #4 - here: https://xdaforums.com/showpost.php?p=77650687&postcount=4

For downgrade you can use HiSuite Method → and you can successfully downgrade to VIE-AL10c00b399SP20

2) After this, you can use HWOTA7 Tool to rebrand to VIE-L29c185 (VIE-L09 would not make sence, because you have DUAL-SIM).

→ You need to download the Firmware for VIE-L29C185B395:

update.zip: http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1891/g1755/v158471/f1/full/update.zip

update_data_full_public.zip: http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1891/g1755/v158471/f1/full/public/update_data_full_public.zip

update_full_VIE-L29_hw_meafnaf.zip: http://update.hicloud.com:8180/TDS/data/files/p3/s15/G1891/g1755/v158471/f1/full/VIE-L29_hw_meafnaf/update_full_VIE-L29_hw_meafnaf.zip

→ Read Post #1 (OP): https://xdaforums.com/p9-plus/development/rebrand-update-tool-hwota7-p9-plus-vie-t3843930/

→ Rename two of the downloaded zip files (it is described in Post #1) and copy it into the update folder C:\HWOTA7\update

→ You need a working USB connection for ADB and Fastboot Mode

3) Here are the steps for Rebranding:

0) Developer Options enabled (7x click on Build-Number in Settings /About phone) - In Developer Options: OEM Unlock, ADB Debugging + USB Debugging (in this order) enabled, HiSuite HDB (in Settings /Adv.Settings /Security) disabled, HiSuite on PC closed, working USB Connection

1) Connect your device with USB to PC and start from HWOTA7 main folder: update_eng.bat - Accept possibly the RSA query on the display of the P9 Plus

2) Restart your P9 Plus into Fastboot mode (use restart/restart and press VOL- /or shutdown phone and press VOL- and Power Button)

→ Note: During all steps USB Cable stays connected between phone and PC and you only press "Enter" in the terminal when the described step, in the line before, was executed.

3) HWOTA7-terminal detects if Bootloader is open or closed - if the Bootloader is closed go to 4) - if the Bootloaer is open go to 7)

4) Terminal ask you for the Unlock code - enter the Unlock code and confirm the Unlock on the phone

5) Your P9 Plus reboots and an automatic factory reset is done with internal storage wipe (lowlevel reset) - wait until the phone reboot to system. Skip everything during setup (except what can not be skipped) - Important: Enable Developer Options with ADB Debugging and USB Debugging

6) Restart your P9 Plus into Fastboot mode - now hit "Enter" Button - HWOTA7 Terminal will flash automatically TWRP for Android 7 and gives you the order to boot into TWRP by pressing VOL+ and Power Button (dont hit "enter" before this step is done)

7) In TWRP swipe to allow system modification - now hit "enter" (2x) in the Terminal - after a short while you will see: Upgrade Options

8) 2. Using script: 2.Change location - you will see a list of available "oeminfo" – in your case use: VIE-L29c185

→ Note: The Firmware for VIE-L29C185B395 (Nougat) must be already in the update folder (and two zip files renamed)!

9) HWOTA7 flashes now oeminfo for VIE-L29c185, Bootloader is getting closed, confirm the Unlock on device - automatic factory reset is executed, wait until 99% and 100% restarts the phone → NOW PRESS VOL+ to boot the phone into TWRP instead of system!

10) Allow system modification in TWRP and hit "Enter" Button for Terminal - HWOTA7 copies now the firmware to the directory: /data/update/HWOTA - restart phone automatically and flashes the Firmware with EVA_RECOVERY_NoCheck.

→ After your P9 Plus has started into the system - you may see a black screen with an input field and a keyboard - if yes, go to 11) - if no, go to 13)

11) Close HWOTA7 Terminal and press Power Button on P9 Plus to restart your Phone, restart phone, in the moment of restart press VOL- Button to boot into Fastboot Mode → Bootloader is closed.

12) Open update_eng.bat, click enter, enter the Unlock code, confirm Unlock on phone, phone makes a Factory reset with lowlevel wipe. Then the P9 Plus starts automatically into the system.

13) Now you have already rebranded to VIE-L29C185B395 (Nougat)

Click enter in Terminal, select 2. "No, I would not" and HWOTA7 will be closed. Disconnect USB from device.

I am not responsible if brick your device, when you do not read OP and follow the steps carefully. And at any point, if you dont know whats to do, write here on which step you are and ask what you do not understand (before you do anything wrong).

I am sorry, I can not help you more. The whole process is easy for advanced users, but difficult if you've never done anything like it. But I do not know how to explain it any better.