Email address for yahoo mail

Will my email address remain the same ie. username@comcasr.net or will it have a yahoo domain. ...

Your Comcast.net email address won't change, you'll just have to sign in to https://login.yahoo.com/ to read and send email from that address instead of using Connect. Or you can use an email program or app with your migrated addresses, once you've accepted the Yahoo terms and have successfully signed in to your Comcast.net email at login.yahoo.com at least once. You'll need set up the email clients using Yahoo Mail server information:

Note that Comcast/Xfinity has been saying over the past week or two that for now at least, migrating to Yahoo is optional and connect.xfinity.com will continue to work until further notice. 

... Hoping I don’t have to updated contact info at all my online account and recovery/2fa addresses

If those addresses are your Comcast.net address they should still work after migration to Yahoo.

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