Gotcha on the intent. It might be better to generate the wall from the face of the existing wall. This will simplify the isolation of the windows and such - they’d already be a part of the wall. For modifying existing wall sketches this may help though: Sketch Lines - Edit, Copy, Paste - #20 by jacob.small
I am curious as to why you’re putting curtain walls in place over solid walls, but perhaps that’s a question for another day.