Instead of building legend editing into GeoNetWeaver we opted instead to use MapWindow GIS to create and edit the legend. MapWindow GIS is a very well supported open source project. It is installed when GeoNetWeaver is installed.
To extract a MapWindow GIS project file from a GeoNetWeaver geoproject:
To import a MapWindow GIS project file into a GeoNetWeaver geoproject:
When importing a MapWindow GIS project file any existing legend in the geoproject is overwritten.