Currently the command key adds any nodes you click or marque over to the set of selected nodes. It doesn't subtract.
It's conventional within Adobe apps and Finder and elsewhere that shift is the modifier key for adding or subtracting from selections with more than one node at a time, while in Finder Command Key allows you to remove or add a single file from a selection of files in a Finder window. I'd prefer that shift be the modifier for adding/removing nodes from the selection using marquee operations for consitancy and familiarity for those of use that use or have used graphics and 3D software a lot. shift for click add/removes too i suppose, or clicks could go to command key I'm not concerned about that.
Currently Option has the curious function of sweeping nodes away to clear an area on the graph canvas, but it just sweeps nodes into a pile on top of each other, perhaps it will be upgraded at a time when expanding and contracting Macros are available to Vuo users. Interested to see what direction that one goes in later on.