Thanks for the reply ANDY, I found a way of doing this by duplicate the sweep nerb with the spline, add a different colour texture, position both on top of one another and then use an object with a transparency material place this over the section you want to punch through (the pink line) add a display tag and chose and untick seen by transparency, this should mask a hole in the pink line and show the other coloured line underneath and add a display tag to the coloured Sweep nerb and untick seen by camera this should give you the pink line minus the
coloured section in one sweep nerb and the coloured line section only on the other sweep nerb I would still like to find if there is a easer way to do this