How do I copy global text substitution settings into iWork '09 (Keynote, Pages)?
The substitutions for Pages.app are stored in:
~/Library/Preferences/com.apple.iWork.Pages.plist

Specifically they are in Root/kSFWPAutoSubstitutionArrayProperty. The format is a an array containing dictionaries with the keys replace, with and on.

The Global Substitutions are located at ~/Library/Preferences/.GlobalPreferences.plist.
Specifically, they are in Root/NSUserReplacementItems. The format, conveniently, is identical.

It's probably possible just to open ~/Library/Preferences/.GlobalPreferences.plist as plain text and copy across what you want into ~/Library/Preferences/com.apple.iWork.Pages.plist.