How can I change my country flag? (ICCforMac/Windows)

Toolbar above: Settings Icon  (or menu above: Edit > Settings). 
Your Options window opens. Choose from the list of options on the left 'Profile'. 
Here you find 'Country Flag' and what it is currently set to. On the right of the current setting you can press on the 'V' for a pop-up list of all the other options.  At the top of this list you can choose 'Dynamic' ('Dynamic' flag based on your current IP address will be used) and 'No Flag'.
 

Command line method: 
To change your flag, type on the command bar under your Console: set fcountry XX   Where XX is the country of your choise. 
Some examples: 
set fcountry US - For United States
set fcountry CA - For Canada
set fcountry ?? - (Default) resets the flag back to 'Dynamic', choosing a flag based on your current IP address.
set fcountry zz - To not show a flag.

To get your console up click on the Console icon  on the bottom (left) of your interface.
Or go to the Menu above, click on 'View' and choose 'Console'.
   
For more information read "help fcountry".