You certainly CAN add borders once you are home, as long as you do so on their full desktop site. You can't add borders to pictures via the app on your phone, but on a computer.....absolutely

. Most of the pictures comes with the standard blue Universal border already on them, but once you sign into your My Universal Photos account on a regular desktop or laptop computer, you will have relevant border options from which to pick.
If you want a specific photo bordered and don't have access to a laptop while travelling (ie you are only using the app on your phone), just stop by the photo store in either US or IOA (or the kiosk in the hub....they are very helpful there too) and ask them to border it for you. They will add the modified picture to your account no problem.
The only thing you can't add at home is the "magic" element: if you happen to have a magic shot taken (you'll know if this is the case, as the photographer will have you hold your empty hands out) then you have to stop at one of the photo stores or the kiosk in the hub and have them add the "magic" element before you leave that day.
We have the annual card.....have had it now 3 times, I think....so if you have any other questions, don't hesitate to ask.