Thank you for your response. What you propose works if one is very happy with the graphics etc.. However, in most cases we want to manipulate the import since some of the graphics often does not work. Or we want to use portions of it as lines and combine it with the real VW drawing/file etc.. We had countless situation where we would have needed to do what Jeff and I were describing.
Also even when export into a separate file and only x-referenced into the main file, e.g. like with a view port reference, we find we have to remove symbols, since they can give problems or make the main file unstable. Also almost all the time we have to change the line colors if we get files from other consultants. In the enormous time pressure we are mostly under often we do not have the time to wait till the consultants react to our request and re-export their files, or they tell us that they do not have the time and resources to change the colors etc.. These are the realities of life when working with a whole army of different consultants on large projects as we do. So often we have to do it from our end in a great rush. Now here with the colors we encounter the same problem: VW does not let me change the colors in one go if the lines are assigned to a class style.