Thanks Keet! All unviewable levels and furniture not flagged as visible are not selected, therefore not rotated. If I manually select all furniture from the list, I end with something completely broken.

I wish SH3D had taggable/alternative branches for levels. Sometimes I want to see different decoration paths, or to see the BEFORE/AFTER on the same project. That's why I heavily use the furniture visibility flag.

The Home Rotator (AKA Plan Rotator?) Plugin seems the best approach. I filed this bug report about the polyline issue.