I have attached an .xml file that uses the code in the cited mod, but requires no template edits. I employed a db query to determine if a user has already rated a thread, and if they have, then they are not asked to rate the thread again, only to be told they have already rated the thread and cannot change their vote.
Simply download the attached file, and then:
In AdminCP go to Plugins & Products -> Manage Products -> Add/Import Product.
Click on "Choose File" and browse to the product .xml file that you downloaded.
Click "Import"
You MUST set your settings to enable the mod.