See http://social.technet.microsoft.com/wiki/contents/articles/13451.customizing-the-rds-title-work-resources-using-powershell-on-windows-server-2012.aspx

If you are running multiple Connection Brokers in High Availability mode, you must run this against the active broker. You can use this command:

Set-RDWorkspace -Name “XYZ Applications” -ConnectionBroker (Get-RDConnectionBrokerHighAvailability).ActiveManagementServer

Otherwise you can use:

set-RDWorkspace -Name “XYZ Applications” -ConnectionBroker broker01.company.local