Can you change your e mail address name and keep all the same information?

Can you keep the old address? More simply, have two e-mails.

If you use Gmail, you can create a new account and import all of your old stuff.

Yes, I think it would depend on the program you are using. Read the Help files on your e-mail provider.

Do you just want to change the name stamped on your outgoing emails or do you want to change your smtp address?
Eitherway, you can change both. If you are going to retire one smtp address and use another you can export the mail and import it into a new profile.
What email client do you use? is it web based or client based like Outlook , thunderbird, etc?

If you start a new email address with the same internet provider it is not a problem. Simply save the address book as whatever kind of file they suggest. You can usually find that command in the “file” tab in the menu bar. Then establish a new email address and import the file you saved. Shouldn’t be a problem. If you are going to use a different email address, meaning switching from one to a yahoo or whatever, just make sure the type of files are readable by both.

As you stated it is Yahoo I will assume you are using the Web client and not POP with Outlook, etc.
If you are only changing the name and not the smtp address in yahoo web client then log into yahoo mail.
Select Options
Accounts
Highlight Yahoo Mail
You will see the From Name listed. Change it. Click Save
Select Return to Mail.
Now anything you send out will be stamped with this name.