Can I change the countries I subscribe to?

This depends on your subscription level.

Starter plan users will have one data stream only and cannot change it.

Plus members can access one country at a time but can change that country/data stream. However, changes are limited to once every 90 days. Choose carefully when you change your data stream. You won't be able to change again for 90 days

However, you can upgrade to Premium at any time and get access to all data streams and avoid the need to change at all.