1) Yes, you can modify the OctaneDefaults.py file to setup the roughness and specular defaults that best suit you.
2) Yes, after modifying the OctaneDefaults.py, reload the scene (forces the defaults to be re-loaded), and then Material Tab->Re-import from Poser and the new defaults will be applied (unless you have saved the Octane nodes to the Poser Material, in which case they will be read).
3) The conversion does not happen because it was not effective
i ask, because the sample i show you is an hair figure with 12+ props to configure
Simply setup your Octane material nodes on one of the hair materials in the Materials Tab of the plugin, then "Copy" that material (right click the material) and "Paste" to all the other materials for that prop. It is a very fast and efficient way of working.