It depends on what your situation is, and it is possible yours is unique and similar to mine.
There are 2 possible scenarios.
- Signing up to any Proton service by creating a Proton Mail address.
- Signing up to any Proton service outside of Proton Mail by using a non-Proton address.
1) USING PROTON SERVICES WITH A PROTON MAIL ADDRESS
In the first situation, which is likely the most common, if you have a paid Proton Mail account, you can create multiple addresses, and make whichever one you prefer your default. You can also change your default address at any point. In addition, when you have a paid Proton Mail account, you can sign in with any of your Proton addresses, even the non-default ones.
2) USING PROTON SERVICES WITH A NON-PROTON ADDRESS (EXTERNAL ACCOUNT)
In the second scenario, when you sign up to any Proton service outside of Proton Mail (Proton Pass, Proton VPN, etc..) you can use any non-Proton address (eg: GMail) as your username.
It’s called an external account.
When you create a Proton Pass account with a non-Proton address, you have an external Proton account, and your username is your email address (jordan.smith@gmail.com).
And when you have an external Proton account, you cannot change your username (your Gmail) to a different non-Proton address. Meaning that if your current username for Proton Pass is jordan.smith@GMAIL.com you cannot change it to jordan.smith@YAHOO.com. Never.
To be clear I am talking about your account username, not your inbox address where emails to your aliases are forwarded. That can always be changed.
When you have an external Proton account, and you want to change your Proton username/email, your only option is to create a Proton Mail address for that account. But understand that once your Proton Pass account is linked to a Proton Mail address, you can never change it back to a non-Proton address.
If you have an external account, I agree 100% that you should be allowed to change your username to a different non-Proton address i.e. from jordan.smith@GMAIL.com to jordan.smith@YAHOO.com. Not being able to do it presents a security issue, especially if the email provider for your username shuts down.
However, if you have a Proton account with Proton Mail address as your username, you can already change it any time you want if you have paid account. All you have to do is create a new address, make it your default, and discard or delete the one you don’t like.
But remember that Proton only lets you delete one Proton Mail address per year. And when you delete an address all of its data gets wiped out, including the emails you received and sent with it. And nobody will be able to reserve that username again.
THE ONE THING I HAVE MINOR DOUBTS ABOUT
Suppose you have Proton Unlimited with 5 Proton Mail addresses managed by your account. Since you can log in to Proton Mail with any of your Proton addresses, I would assume it is the same with Proton pass and Proton VPN. Meaning that if jordan.amith@pm.me is your default Proton address, and fresh.cow@pm.me is your second address, you should be able to sign in to Proton Pass and Proton VPN with the latter too. I don’t see why it wouldn’t be the case if you have Proton Unlimited or Protn Mail Plus.