This kind of stuff is just awesome, and an important keybinding to remember is Cmd-U (I'm on a Mac) to undo bad selection decisions. But the situation is not so optimal as-is.
So I've got many occurrences of the same word selected with Cmd-D. Next thing I see is that I don't want a certain word selected. How subtract selection currently works is that I have to (somehow) start the de-selection process outside of a selection and drag over it while holding Cmd-Shift. That is just uncool. What is cool is that if the selection is the only one on the line, I can Cmd-Shift-triple-click outside of it to remove it. Way to go!
How I would improve this: I'd like to be able to remove a selected word by Cmd-Shift-double-clicking it (i.e. inside the selection). What it currently does instead is the same as if I just single-clicked at that location: The (single) cursor goes there.
Another thing is if I have just multiple cursors (no selections), I'd like to be able to Cmd-Shift-single-click one of the cursors to remove it. But, same as above, it currently just places the (single) cursor at that location.
Feedback, workarounds (other than using Cmd-U and then doing it the right way - I'm looking for speeding-up workarounds here), plugin (programming) suggestions and bugfixes are all welcome! I love it that the annoying things about this editor are in the tiny minority. Keep it up!