You can actually edit your SU lines if you
turn vector or hybrid rendering on (the default is raster)*
then explode the SU drawing in LO - then the model will act like deeply nested groups in SU so you need to double click to edit until you can select the individual set of edges.
http://lh6.ggpht.com/_zcvsIuYiVbo/S2pCbqJ1J2I/AAAAAAAADZg/5W9pPSpMj7E/LOShapeStyle.jpg
Note that this (exploding) is a destructive and irreversible operation which will ultimately beak the linkage between that particular SU viewport in LO and the embedded skp file so only do this when you know you are ready with the modelling phase.
Of course, you can always delete just that exploded viewport and insert the skp file again - the model itself won't be affected this way.
if you explode it while raster rendering is on, it will become an image that you can open/edit in an external application and it will instantly reload upon saving.
