Yes of course you can do that in Pages (and in other apps on a Mac). You just don't know how (yet), but you will by the end of this post.
The problem is that that's NOT the definition of "predictive text," so naturally I didn't understand what you wanted. What you want is a Macro.
To do this in Pages (and most other standard Apple applications on a Mac):
1. Open System Preference and select "Language and Text."
2. Click on the "Text" tab.
3. Use the "plus" button at the bottom of the preset list to add, edit and generally manage any custom word/phrase shortcuts you want to have.
IOW, it works pretty much the same way it does on the iPad.