Is it possible to move a Stack Exchange account from an existing (Yahoo) login to native Stack Exchange login...?
I'd rather get rid of the email account linked with my Stack Exchange account but keep the latter.
Technically, there is no native Stack Exchange login.
To quote myself from my answer to Login username/password for Stack Overflow on Meta.Stackoverflow:
Technically, Stack Overflow does not have a dedicated login system. They have chosen to support OpenID (and OAuth 2.0 on a few places). Given Google has deprecated OpenID in favor of OAuth, I am assuming that OAuth will become more supported on Stack Exchange sites.
However, Stack Exchange does have their own OpenID endpoint, so in a sense, that is the closest to a dedicated Stack Overflow login.
To paraphrase the rest, there used to be a way to add a Stack Exchange OpenId as a login to an existing account, but for some reason, the option no longer exists. You can only use it to create a new account (it might be a bug or it might not, that hasn't been made clear).
Worst case, you can reach out to the SE team by clicking the "contact us" link in the footer of every page and they will be able to help you out.
It sort of works, though it is a little more convoluted that it could be.
You'd need to start by creating an account at the Stack Exchange OpenID page.
Login, check your profile page, and click on the link "Use your own URL to log in".
It'll give you a bit of HTML code
You need to copy the link on the second line
Now go to your profile, My logins, add more logins
And paste that into manually enter your openid.
Its detected as an SE login, and is handy when you stupidly delete yours testing things, like I did.