Authors to be able to customize their author pages?

So if i understand correctly you want to let the authors style their profile and save the data in a way that every visitor will see their saved style, kind of like twitter lets you style your own author page. If so then using cookies won’t help you here since cookies are user specific and not saved on your server or in the database do you won’t be able to generate the style the author has picked anywhere but on that authors browser.

What you should do is save all of the style data as an array in the usermeta table using add_user_meta() or update_user_meta() and then on your author page call that array of data using get_user_meta and generate the style the user has picked for his author page.