CTRL + C

[B.Y.O.B.]

Apparently this bug is already fixed in the latest Blender master (available from builder.blender.org).
Unfortunately, BlendLuxCore can only be enabled on Linux when using the master (not on Windows due to Python version incompatibility).
@Racleborg: If you are on Linux, you can try this. Tell me if you need more detailed steps.

[Racleborg]

B.Y.O.B
I'm not on Linux, but no worries and thank you for the information.

[Luxart]

Luxart.

Yes, LINK. Thanks
Is it possible to break the LINK, otherwise it acts like a standard CAD sub-assembly and if the original is modified then so is the copy?

Then you can simply Append. The appended object is not affected by the changes in original file.

You can google about these basic operations in blender. you will get additional info from it.