Have you tried applying the pending changes? It looks like in the example above you are setting and then getting immediately, without applying the changes?
Note: After setting a configuration key value you must apply the pending configuration changes using
tsm pending-changes apply. Until you do, the new value will not be used by Tableau or show up in the results of a
tsm configuration getcommand. You can view pending changes using
tsm pending-changes list. For more information, see tsm pending-changes.