You're very welcome.
The plugin preferences will survive plugins being uninstalled and newer versions being installed. So unless you specifically delete the plugin's preference file, you shouldn't need to worry about redoing the tweak. If you install Sigil on a new machine (or under a different user account), the instructions will come in handy, though. I'll also document the tweaks on the first post of this thread whenever I "officially" update to this new version.
Thanks for reporting back.