From what I've read, the Wii doesn't just use a CRC check on it's data files but encrypts them as well. Has anyone developed a tool to decrypt/encrypt data files? The file extension is a DAT file, and it's easy enough to note the different current game stats, then use a hex editor on the DAT file and find those values. However, changing anything in the file, then reinstalling the modded file leads to corrupted game files. At first I thought CRC, but then a little searching indicated encryption.

Nearly every encryption algorithm operates on sequences of bytes and spread out to prevent the attack you are describing. That is, multiple raw bytes of data are combined to form one encrypted byte and then when decoding multiple encrypted bytes are needed to decrypt a single data byte. So even if you had two gamesaves with one minor difference between the two, there would then be significant differences in the files.