If you wanted to change global anti-aliasing threshold to 16, you'd do:
defaults write NSGlobalDomain AppleAntiAliasingThreshold 16
at the terminal prompt.
If you wanted to change it for say just Safari, you'd do
defaults write com.apple.safari AppleAntiAliasingThreshold 16
or for Word:
defaults write com.microsoft.Word AppleAntiAliasingThreshold 14
You can find out the name of the domain to use by looking in your ~/Library/Preferences folder. In there you'll see all the preference files for the applications you run, typically with the naming convention of:
com.<company name>.<App Name>.plist
Have fun!