Install OS X High Sierra without converting to APFS file system

install-osx-high-sierra-command-line.sh

# create a USB installer
# https://support.apple.com/en-au/HT201372

Download the OS X High Sierra installer via the App Store, it will be installed into the /Applications directory
If it opens automatically, close it
Insert a USB stick (8GB+)
Run the following command where MyVolume is the name of the USB volume:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

# boot the USB installer

Boot the computer holding the Option key
Select the USB installer as the startup disk

# from the menu, select Utilities > Terminal
# install without APFS (optional)
# use the installpackage parameter to install an extra .pkg (optional)

/Volumes/Image\ Volume\Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall \
  --volume /Volumes/Macintosh\ HD/ \
  --converttoapfs NO \
  --applicationpath /Volumes/Image\ Volume\Install\ macOS\ High\ Sierra.app \
  --agreetolicense \
  --installpackage extra-package.pkg