Tags in iTunes 12

I'm running OS X 10.10.2 with iTunes running 12.1.2. I would like to know if there is any way to add and remove the 'explicit' and 'clean' tags to my music in iTunes. They have been dowloaded and not purchased from ITunes so not all them have these tags. I would like to know how to add these tags so it appears in my iTunes library next to the song and in the 'now playing' bar. I would also like them to show on my iPhone (5s, iOS 8.3) and iPad (2, iOS 8.1).

Any help would be much appreciated.