Press Alt+Tab until you've placed the keyboard focus, as shown by the highlight, on the Front Panel.
Press the arrow keys to move the highlight to the button for the workspace you want to rename.
Press Shift+F10 to display the workspace button's pop-up menu.
Press the Down Arrow key to select Rename, then press Return.
The button becomes a text field.
Edit the workspace's name in the text field.
Once you've renamed the workspace, press Return.