All existing forum entry metadata will be replaced with the new data. To avoid deleting all existing data, retrieve any data you want to retain first, and send it back with this request. See Retrieving forums for more information.
If you want to lock the forum, add the element <category scheme="http://www.ibm.com/xmlns/prod/sn/flags" term="locked"/> in the forum entry that you pass in as input. If you want to unlock a forum, remove the same element from the forum entry that you pass in as input.