Is there a way to change the thickness of the back stitching for different parts of the pattern? e.g... thin lines in some parts of the pattern and thick lines in other parts.
I don't think you can change the thickness but you can change the style - based on color.
You can't do it from section to section unless you are referring to a different symbol. Even if it is the same color, it is considered different if it has a different symbol.