I haven't tried doing this in quite some time (iTunes 7 era), but I seem to remember simply editing the XML file iTunes creates was NOT sufficient in updating the Date Added field in iTunes.
In case you're curious why I would want to edit Date Added, it is because I most often enjoy listening to music with iTunes sorted on Date Added field. Most of the time this is a logical order for me, but occasionally (when importing more than one album at a time) iTunes imports a batch of songs in a seemingly random order, so I might have very differing albums intermixed. In these cases, I'd like to go in and make sure the Date Added times are grouped by album.
Best Answer
Just change the system clock and add the file again: