To change the RD Workspace name you need to run the following PowerShell Cmds.
Import RDS PowerShell Module:
Import-module RemoteDesktop
Set the RDWorkspace name:
Set-RDWorkspace -Name "<Name you would like>"
Example:
Set-RDWorkspace -Name "Ryan Mangan"
Check RDWorkspace name:
Get-Workspace -ConnectionBroker <Server FQDN>
Ryan Mangan's IT Blog 
That’s great! Thank you very much for this post!
The above method does change the name on the main page but if you have enable the Password Reset Utility the name still shows up as “Work Resources”.
It’s a different page