Sending, receiving, and organizing email in Outlook.com
You should be able to continue using Outlook without changing your email address. Although the mailbox is now hosted by Yahoo, you can add the existing Comcast/Xfinity address to Outlook as a Yahoo account.
In Outlook, select Add Account, enter your full Comcast/Xfinity email address, and choose Yahoo as the provider if prompted. Complete the Yahoo sign-in and permission steps to connect the mailbox.
Before doing this, make sure you can sign in to Yahoo Mail using the same Comcast/Xfinity address. If Yahoo does not accept the account, you will need to contact Xfinity or Yahoo because they now manage the mailbox and authentication.
I hope my answer helps. Have a lovely day