I back my stuff up just in case, but you shouldn't need to. Really, if you don't mind bubbles resetting their position, it'll be fine. Turn off your Vita, take out the memory card(MAKE SURE TO DO THIS), turn it back on, do a system restore(and thus deactivate your main account), then go through the first time setup again. But instead of putting the log-in information of your main account, you want to use the email and pass for your JPN account. When the stupidly long intro video is done, turn off your Vita again and put in your other memory card(4gb). Should be good to d/l things from there. Make sure to get the Project Diva f demo!