with the tres keyword it should invoke an applescript to
1 - open system preferences
2 - select the Displays preference
3 - select the Color LCD Tab
4 - Click the Scaled option
Once there it will look at the options presented and detect the state of radio button 3 "Best for Retina"
if it is selected then it will choose the 5th radio button ("More Space") if it is not selected then it will select it
Then it closes system preferences.
This is all on a 15" Retina Macbook Pro running 10.8.3. The panels for the display preferences has changed around a bit in the various versions so it's worth checking you OS version
