Here’s how you can change the email address you use as your Things Cloud username.
There is no way to automatically switch your account from one email address (username) to another, but you can achieve the same result by deleting your existing account and creating a new one with a different address.
When you delete your Things Cloud account, only the data in Things Cloud is deleted. The data which is stored locally on your devices is not affected.
Once the new account is created, Things will automatically upload your to-dos into it. Then just sign into this new account from your other devices, and you’re good to go.