Set the Plays ("Play Count" before iTunes v9.2) of the selected tracks to a user-entered number (they will all be set to the same number). If this number is 0 then the Last Played date of each track will be erased. (iTunes has the ability to "Reset Plays" to 0 from a track's contextual menu.)
Also see New Last Played Date and Add or Subtract Play Count.
Remove iTunes tracks disassociated from files
Export files of tracks in two or more playlists to single folder
Append user-entered text to beginning or ending of selected tag of each selected track
Batch set new Last Played/Last Skipped of selected tracks
Enter text for the selected tracks' Description tag
Set the Plays of selected tracks.