I have already explained how to edit symbols and wire thickness on an individual basis, for clarity of purpose sometimes this is something a designer might want to do.
KiCad is a first class CAD package and excellent for schematic and PCB design but if you need something for making big pictures, a graphics package would be more suitable.
Alternatively, you could try printing the schematic to a file and post-editing it with a graphics package but I can't advise on which may be suitable.
Brian.