Ah! Score one for Inkscape then, as its xml editor will let me edit them. Then take points off because I've just discovered while breaking bendable legs that Inkscape changes the order it writes xml out apparantly at random (i.e. the fields are there and the same, just in a different order so if you diff the two files you get a mass of changes most not relevant) or even realy there.) I'm back to the perl xml parser to see if I can make something fairly easy to actually do a useful diff of two Inkscape files so I can see what is changing. The joys of parts creation 
Peter Van Epp