PreMade Objets imported from STL files have significant changes when imported as segmentations

[cpinter (Csaba Pinter)]

If I understand the problem, then I just described the solution earlier today to someone else (it’s enough to just look at the bullet points):

Difficulty with editing new segments imported as stl files

In your second screenshot you cannot edit because there is no anatomical volume selected. That’s why Segment Editor is asking you to “Select master volume to enable editing”, as shown in your screenshot as well. In the third case, I can see a master volume. If that “6: CHEST…” image occupies the same space in 3D as your imported STL, then you should be able to edit it. You can verify that by going to Volume Rendering and showing the CT in 3D. If “chaos breaks loose” means what you described ne…

It’s not the easiest workflow I know, but right now this is the best way to do it.