The previous link is updated too.
I made a few changes and now it seems to be working.
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@Keet Thanks, you've encouraged me!
The plugin (like SH3D) does not work directly with obj files.
-Exports the furniture as obj+mtl+texture to a temporary zip file;
-Loads it back as BranchGroup;
-Extracts the geometries from it and creates an Object3D (a kind of solid);
-Perform Boolean operations with two Object3D;
-Perform the steps in reverse order until the new furniture is added to home.
The XOR operations still don't work as expected.
Even so, use it with care!