I'm an architect. I export a building model from my architectural application in 3ds format, and import it in blender. Everything works fine. Now suppose that I make some changes to the original model and re export it. Can I update the existing model in blender keeping all the materials, lights etc?
If this is not possible, at least can delete the old model and import the new one, keeping the materials as modified?
When you look at your material names in the material node panel to the right you will see a number, that is how many users of the material are in the project. Then to the right of this is the letter F
. This will Save your material whether or not it is being used. If you want to keep all of your materials, then go into each one and click this button. Another way you can use this is to get rid of unused material when you're experimenting. Save the ones you want, save the project and close. Then, re-open and the unused materials will go away.
As for updating the model you will have to delete and re-import each time. Once you Import or Append a model it becomes a new instance in that project. But, all you will have to do is re-attach the materials to it. You may want to name your materials in 3DS to similar names if they show up in Blender to make it easier to keep up with which objects have what material.
Hope that helps.