The RB file supplied in the post above is ‘half-baked’ - it’s only the registration file for the main code in ‘copy_main’ which will be in a subfolder with the same name as the extension RB itself. So you get the error. You need to install the full set of files and the subfolder from its RBZ. Even if you had the main code the toolbar would be FUBAR because the icon would be missing etc…
Someone should post the RBZ, or link to it properly !
There are plenty of things that could be added or improved about Sketchup. Adding variations and splitting up one of it’s slickest and most elegant commands is not one of them.
Also, this could be set up as a ruby, autohotkey or similar script that just triggers your move tool shortcut, waits 100ms and then triggers control and/or make unique. It would take about 5 minutes using any free LLM.