You mean linking your Vita to your PSN account after you've gone through the initial setup? Yes, there is. Give me a few minutes to grab my Vita and I'll update this post with the directions.
From your home page, go to Settings >> PlayStation Network. (Granted, mine is already sync'd, so I can't see the initial steps). Everything you need will be under the PlayStation Network section (change account information, update your profile, system activation, etc.)
Hope that helps!