Change email name on icloud.

You could do one to two things:

You could set up an alias email address which is part of your current account. Apple describes how in this support document. In your example that alias would be bob.taylor@icloud.com and incoming mail to that address would be delivered to the In box of the existing account bob44@icloud.com and you would cease using the bob44 address and instead use the bob.taylor address.

The second option is to change your Apple ID. See the Apple support document of the same name here. This is typically used by people who have lost access to the email address which forms their Apple ID. As Apple describes this problem: If you no longer use the email address that's associated with your Apple ID, you can change it. You won’t lose access to your contacts, purchases, or other account information.

That document goes on to detail how you achieve the changing of your Apple ID. Be aware though that as your ID has changed you will have to sign in again on your devices using that new Apple ID address.

However, I'm not sure that you can change an @icloud Apple ID to another one, if that is what you are proposing to do.