Sony has addressed recent stories that the PlayStation Vita can only support a single PSN profile, declaring that you can have as many accounts as you like ... if you've got enough memory cards. It turns out that PSN profiles are tied not to the system, but to the memory card inside. You want a second profile? Buy another card.
“Your PSN ID is bonded to your memory card and your memory card is bonded to your Vita," a PSN rep told Wired. "So if you wanted to change different PSN users but use the same memory card, you would need to go factory reset."
So, the factory reset method is only if you have a single card. Of course, considering how pricey those memory cards are looking, this probably isn't an ideal solution for users who like to have a PSN ID from each region. Not that Sony cares, because dollars, son.