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 Add or Subtract Play Count.
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Remove iTunes tracks disassociated from files
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Displays files in iTunes Media folder not in iTunes track library
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Copy Artist to Album Artist of selected tracks
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Add or subtract a user-entered number from each selected track's Skip Count
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Append user-entered text to beginning or ending of selected tag of each selected track