It is not possible at the moment to set the country IP address when using the Tor tab.
This has the following issue; If creating an online account, the website usually checks the country you’re connecting from. So if creating an account using a Tor tab, your account will be linked with a specific country. If then (later) you try to return to that website, you will probably get blocked due to suspicious behaviour, as in, your ip address changed to quickly for you to be able to fly to another country in a matter of minutes.
Therefore, I feel it will be very beneficial for brave users, if they can set IP addresses to be country specific when needed.