Per,
Go to your library and add a field with the drop down value you want displayed. Then go back to your content organizer and define the rules based on the choices you put in that field. That should give you what you are looking for. You can define a rule that checks the title for key words such as “test” or “math” or whatever and use the rules that way, but a drop down field is easier to setup and use.
Let me know if that helps.
Eric