Set text for macOS floating text screensaver from command line
this thread is no.1 in Google for "macOS screensaver text" query, so I decided to put my answer here.

Currently (macOS High Sierra 10.13.5) if you want to change the text of your "basic" screensaver you have to type:

defaults write ${HOME}/Library/Preferences/ByHost/com.apple.ScreenSaver.Basic.plist MESSAGE "your message"


after that it's necessary to reload:

killall cfprefsd


after that you can test your changes with running a Screen Saver from a command line:

/System/Library/CoreServices/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine


For my needs I wrote a small script that inserts a ten-minute time interval in the screen saver (to show how long the break takes). It's here macOS ScreenSaver Text.

Hope this helps someone. Cheers.