I dont think there is option to add more than one geographic country but i would say that you should not think that it can help you to get traffic from those targeted countries. The only way to get traffic from those country is to optimize your website locally.
You can do one thing... Although it might sound a little bit crazy but you can switch the geo targets after 6 months and see which one works better! Keep the one which you think is working better..
Sort of like doing A/B Testing Good Luck!
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