How can I globally disable 'Text Replacement'?
Very late, but 

defaults write -g WebAutomaticTextReplacementEnabled -bool false


Will disable text replacement not just in Safari but in all other apps that use that input method (e.g. Evernote). 

Reboot is required (at least as of macOS 10.13.6), and the menubar checkmark UI won't visually change within each app. The change also only affects applications, and not Spotlight.