XDA is open for everyone, on those Chinese forums they keep their resources well hidden, but they don't bother thanking the people here on XDA for their work (rooting tools maybe?), and they even get credits for the tools taken from here! --rant over--
Let's start now. This guide is for all user of D857 or D858 wanting the Google Apps on their phones without messing around with rooting and custom recoveries, but want to keep the phone in a stock condition. Model D858HK is the only Dual Sim officially supporting the GApps, the goal of this guide is transforming a D857/D858 into an HK model.
Enable USB debugging on your device: menu > settings > developer options.
Install Stump Root and root the phone. Install SuperSU immediately after reboot and run it.
Install Build Prop Editor apk (I used Build Prop Editor from joeykrim, the other one didn't work), edit ro.product.model=LG-D857 to ro.product.model=LG-D858HK.
Install LG Driver.
Install LGFlashTool, overwrite the megalock.dll with the provided one.
Turn off phone, hold the volume up key and plug into the computer (DOWNLOAD MODE).
Let the LG driver install for your phone.
Go to device manager in Windows Control Panel, change LGE Mobile USB Serial Port to com41
Open LGFlashTool select the right TOT file and dll (use BOARD DL)
Go to Port settings set LIMO Port to COM101 tick port 1 only on the right (Basically first 3 items ticked)
Remove the cable for 5 seconds and reconnect, the flash will start
Now you have a D858HK instead of D857.
If you get a port error at the starting of the flash disconnect the phone, remove LG drivers, reinstall them again, change the port to com41, and without rebooting launch again the flashtool.
If you get a Windows error, remove any antivirus you have!!
If at the end of the flashing procedure the phone boots into the miniOS, then pull out the battery and enter into the recovery and do a factory reset. Reboot. When in miniOS again, press the power button and tap on normal boot!
ALL-IN-ONE TRANSFORMATION PACKAGE (thanks to ikol-77):
TOT File (D858HK v10d)
Alternate link (magnet): magnet:?xt=urn:btih:8643A5C8F6F5B12A...a80%2fannounce
Alternate Link with Blindfolded XML for Flashtool (magnet): magnet:?xt=urn:btih:6D5F4E34FF96E104...a80%2fannounce
Build Prop Editor v1.17
LG Driver v3.12.3
LG FlashTool v184.108.40.2067
Alternate Link (magnet): magnet:?xt=urn:btih:2037B01DADF1D36D...a80%2fannounce
Stump Root v1.2.0
IMPORTANT: For those of you with not working links or different issues during the procedure, please have a look at the findings of reb00tz (again, thanks buddy!):
For those of you needing to root, here is my guide, just follow it without installing the GApps, it's useless now!
DO NOT INSTALL v10c on the D857, it's impossible to root at the moment. If you do, the only way to go is the downgrade.
Will edit with more detailed instructions soon. STAY TUNED!
Edit: Thanks to member biu40288 on gfan, here is the newest v10f D858HK:
Alternate Link (magnet): magnet:?xt=urn:btih:D0B7D6F43FDC1361...a80%2fannounce
WARNING: v10f no root! None of the root methods work (PurpleDrake, IoRoot, StumpRoot, Tow3lRoot)!
If you need to go back to v10a of D857, here are the links thanks to ikol-77:
LOLLIPOP D858HK v20d: http://csmgdl.lgmobile.com/dn/downlo...58HK20d_00.kdz
Video-Guide for flashing the LG G3: