Several versions ago (probably in the 5.x range or so), it used to be possible to copy and paste a selection from one design into another file that's open via a second instance of Sweethome3D. I can't seem to do this anymore, but I can't recall when the behavior changed.

Is there any way to accomplish this or something similar in 7.1?

I have several versions of a design that I'd like to combine various parts of into a new file, and would prefer not to have to painstakingly recreate things.

I'm on Linux (an Ubuntu derivative) if that matters.