How to Modify AppleGraphicsDevicePolicy.kext ？

[idaima]

I do not know how to modify AppleGraphicsDevicePolicy.kext make support for external hdmi monitor, can you give me some advice??
Thank you!

[idaima]

I find this method , close issue ~
HDMI/VGA Video-Out Fix for iMac7,1 or MBP13,3

Open /System/Library/Extensions/AppleGraphicsControl.kext/Contents/PlugIns/AppleGraphicsDevicePolicy.kext/Contents/Info.plist
Find the Board-ID which used in your config.plist, default in this tutorial is "Mac-B809C3757DA9BB8D". Differs when using different smbios.
Replace the attribute Config2 with none
sudo kextcache -system-prelinked-kernel && sudo kextcache -system-caches
reboot