To change a property for multiple guests in a single operation:
1.Select multiple guests in the 
Guests, 
Groups, 
Floor plan, 
Table plan or 
Schematic panes using 
+click/
+click (+A to select all). Note that you can select tables or groups to edit the properties of all guests sat at those tables or belonging to those groups.
2.Select Edit>Guest Property and then choose the appropriate property and value. Choosing ... will display the Edit Guest Property window.
See also:
•
Edit multiple guest properties (video with audio, 1:48 minutes)