I recently wanted to chamfer all edges of a part but leave just one edge unchamfered.
I couldn't find an easy way to do this other than selecting the whole contour, selecting the complete contour again so it turns red, clicking the U-shaped icon in the HUD, selecting all the edges I wanted chamfered leaving only a single edge unselected and then clicking the green 'plus' sign to add the selected edges to the contour. Although this worked, it could be a long-winded effort, especially if there are many edges or small edges that are easily missed.
Would it be possible to have an extra option via the HUD where you could select the one (or more) edge you didn't want and then click a button to select the inverse of what you have highlighted?