A NeoGAF forum member has reported that information handed out at a PS Vita preview event they attended in Osaka, Japan states that only one PSN ID can be set up on a PS Vita console at any one time. Furthermore, based on the user's translation of a Japanese FAQ, swapping between PSN accounts on Vita is only possible if the console is first formatted to factory settings.
The NeoGAF user's translation reads:
Q: How many PSN account can be set up on a Vita system?
A: Only 1 account. If you want to to use a different account, you need to format the system to factory settings.
That only one active PSN ID is permitted per handheld is no great surprise, as the PSP is set up in the same way. However, with PSP, the PSN account associated with the device can be deleted and the handheld linked to another account and its associated content without too much hassle. If this translation is accurate it suggests the only way to link a new PSN ID to Vita – for example, to enable multiple family members to access their PSN content and trophy information via Vita or for Vita owners to purchase PS Store content from other regions – is to first format the device to factory settings.
IGN has contacted Sony for comment.