You could backup your data before you format by plugging your sd card into a PC and copying everything on it into a folder. Then you could put it back later either on a different or the same sd card if you wanted to use it on your console again. Just don't tamper with the console the data belongs (or your data will become incompatible). If you just want to backup your USUM game, you could try locating it's save directory and backing up just that one folder to put it back later. Though backing up everything is easier and safer.