I've now ditched the branded/old Cura 2.3.1 version that I've been using for almost a year now and have just installed the native Cura 3.3.1 OSX version and have been playing with the
Settings -> Special Modes -> Relative Extrusion feature. I'll have to say that this really starts making post-processing scripts a lot easier now.
I've just rev'd my GetToDahChoppa program (and will push it soon enough) to chop this Scrabble tile into two gcode files from the new Cura. The first is white and the second, black.