Those settings are supposed to only be used when new objects are added to the network. Since the Network is Dref'ed you cannot be adding to it, therefor there should be no reason to be editing those settings, hence them being uneditable. However, the Dref'ed network SHOULD update the layer settings based on the Source network's settings when they change, but they do not. This, IMHO, is where the bug is in this regard. As for the layers changing when synchronizing, I, and others, have told Autodesk that this is not desirable behavior. I think I saw something about C3D2015 changed how this works.
Short of deleting the DRef, setting the default ObjctLayerSettings correctly, and reimporting , I don't know of any way to 'fix' this.
Note that you can change the Styles used by the network parts and those will persist when a synchronization occurs. So perhaps you can accomplish what you need via this avenue?