Is there a way to make the outlines noisy / wiggly without modifying the geo?
For example having a simple sphere whete the outline instead of a perfect circle is a wobbly line, not exactly following geometry?
Not sure about 'wiggly' but you can certainly break up the edges/silhouette with:
cell_noise -> edge-> silhouette-> width_scale
Example at the bottom here.
You could maybe fudge the wiggle by displacing a transparent duplicate object.
h, the latter is what I wanted to avoid. That solution definitely works but I was wondering if there was a way to just displace the lines instead of the geo ?
Another approach would be a compositing one: render at least two passes, one with lines and one with shading, GI, etc. Displace the lines over the shaded pass in your compositing app.