I'd like the option to add small positive or negative weights to intersections / roads I know to be problematic.

Generally I also prefer to stick to more major roads unless there's a major time savings (E.G. >= 5 min, this is part of 'how aggressive' you propose) or accident.

The other aspect of aggressive would be the relative cost for 'unusual movement', such as (legal) U turns, cutting across on small side street connections rather than a major intersection, etc.