Most convenient method to switch between PSN accounts to access PS Vita content from different Playstation Stores?
You can have two different memory cards, one for each user, but you will need to do a factory reset each time you swtich your memory cards, see the following video, courtesy of IGN:
Do a backup of each different region PSN account you login to a PC. Then if you want to switch, just load that specific save file. No need hastle of restoring factory settings or buying another memory card / Vita etc.
Only down side is that you must have access to a PC to switch ...