Apple Mail supports adding additional email addresses by separating them with a comma. But unfortunately there is no GUI functionality for having a second “From” name.

Editing Accounts.plist will allow it tough:

Insert into ~/Library/Mail/V2/MailData/Accounts.plist into same level as <key>EmailAddresses</key>:

<key>EmailAliases</key>
<array>
<dict>
<key>alias</key>
<string>YOUR.ICLOUD.ALIAS@me.com</string>
<key>name</key>
<string>YOUR NAME</string>
<dict>
<dict>
<key>alias</key>
<string>YOUR.ICLOUD.ALIAS@icloud.com</string>
<key>name</key>
<string>YOUR NAME</string>
<dict>
<array>