Well, am trying once again to figure this out. I have searched this forum in vain. I realize that most of what I need to do can be done with regular expressions, but since I don't understand how that works, I can't simply write one. I also can't find one already there to fit my needs.
Right now, I need the export to do two things that it is not doing:
Format the date properly. "6/3/2013" should be formatted as "Mon, 03 June 2013 15:21:19 GMT"
There is no built-in function in MP3tag that transforms a simple date in such a was as you described it.
If you need "any" date you may use the file_create_date or a similar variable. You would then have to find a programme that calculates the day of the week out of this date.