Is there any way to add the "Explicit" sign on a song on iTunes?

When buying songs off the iTunes Store, there are some songs tagged with either [EXPLICIT] or [CLEAN]. How do I add either of these tags to songs that I did not buy from iTunes? And I'm not talking about merely adding the text "explicit" into Comments or Grouping field in songs' Info. So far I have only found in Google solutions for Macs but not Windows. If Mac can do this with a few of the Macintosh-only applications, then there should be a way for Windows to do the same thing.