Yes, Definitely you can unblock the country which you blocked. You can unblock that country by using remove the country from the blocked list and Save the settings. Now you can access the store by your country.
So in the Easy Country Blocker app, you will not face any kind of problem blocking or unblocking the Countries/States.
Install the app from here.
Shopify: https://apps.shopify.com/country-blocker-1
Bigcommerce: https://www.bigcommerce.com/apps/easy-country-blocker/