Core.pkg? anymore information about this méthodologie (a link may be?)
- Right Click downloaded 'Install macOS High Sierra Beta.app' and select 'Show Package Contents'
- Now navigate to 'Contents/SharedSupport' and mount 'InstallESD.dmg'
- Run 'Core.pkg' from 'Packages' folder and install High Sierra
- When it finish installing, navigate to 'Contents/SharedSupport' once again and mount 'BaseSystem.dmg'
- Navigate to 'System/Library/CoreServices' and copy 'boot.efi' and paste it to same path on your installed High Sierra HDD or SDD
- Now reboot and enjoy
This installation method will not update your Recovery HD to High Sierra and it will not show any option to convert target partition / drive to APFS during setup. I tried APFS on my SDD by installing High Sierra twice using 'Core.pkg', it works, but there's no noticeable performance difference for me and it makes re-partitioning the drive bit complicated, so for now I prefer HFS+