I can view the properties (right click, properties, details) of a video file and it has a field for parental rating.

How can I add a rating to the file (the field is blank)?

There is the problem that if I can add a rating, someone else may be able to change it to circumvent parental controls on a video player. This isn't of concern to me at this time.

Edit: The file types are both .avi and .mpg.

Edit 2: I own the file and have 'full control'.