If you give the RUI file the exact same name as the plug-in RHP file and install it in the folder containing the RHP file (or its parent folder) Rhino will automatically stage it in a writable location and open it at startup.
Thank you for the info and the magic!. I have been trying various registry entries on my own in the meanwhile. I think I might have stumbled upon the following registry entry…
If I append the following key value to the location of the RUI file (in a writeable location), Rhino is able to display the toolbar automatically.
Can I use this method? Also, while un-installing the plugin, I can delete the entries to reset the toolbars. Is it the right way to de-register the toolbar while un-installing?