Is there a good way to duplicate a complete namespace in dokuwiki? Could not find a good plugin or method. I do have access to the wiki itself and the backend.
You can do it on file level, this is one of the strength of the DokuWiki engine. Just go to the data/pages directory, and copy the directory and files either in command line or with the GUI. You can do any other file operation, to modify or edit the content. Note that you may need to reindex after the operation, with bin/indexer.php, or there is a plugin for that also.