An unrelated method of tracking shortlisted players categorically is to create a note for each one. It's not sortable in the shortlist screen, which probably adds too many mouseclicks, but it's a "band-aid" method.
- Go to your shortlist
- For each player on the list, click his name
- From available actions, click create note
- In the note field, enter the category you'd want the shortlist to contain like "prospect" or "veteran". You can also enter whatever text in the text field you wish regarding the guy
- The note is automatically saved and updated
Now you'll have a list of created notes for each player that are, by themselves, sortable, since the create note system saves the player name automatically. This is also useful to give yourself a reminder to attempt a trade, promote a player in your system, or set a general reminder to review a shortlisted player periodically. Again, it's outside the shortlist screen, but for now, it might be your best option.