I've added the option to disable the right-click in inventory feature and also an option to require a special permission to use it. By default this last option comes disabled, but if you want to enable it make sure you give your players the permission 'bettershulkerboxes.use.rightclick'

If you're using Spigot 1.14.4 builds please make sure you're using the latest, previous versions cause the plugin to fail when closing shulkerboxes, which means duping.