What I'm trying to do, is change the tuning of the instrument, but not the note. (So if I had an open note on the E string (0), then I dropped the tuning to a D, the note would move thus (2))
I've been told there is some sort of transpose button, but I can't find it. Can someone help me?
At the same window you change the tuning, you have to see the checkbox option: "Transpose afected notes"
This option checked will move the old (0) note to (2) as you expect.
If you can't see this feature is because you have an older (<1.2) version of the application.