Copy address book group between aliases

You have to treat each one as a separate account, just like if it was from Yahoo or Gmail.   To copy the address book, open it and then on the landing page click on "Address book" in the left pane to select it, then on the "hamburger" icon to the right of it.  There you will see the option to export it.  You would then export it as a .csv file to your computer.  From the other account you would then reverse the process and import the file.  And just to add-------if you are referring to Comcast secondary accounts, they are not aliases.  Comcast email has no provision for using traditional aliases. 

Thank you. That was educational. I've been under the wrong impression for quite some time.