Actually, it isn't all that hard to reverse-engineer a data file format, having done so several times. As long as the data isn't encrypted, it is almost guaranteed that there will be patterns to the data. Once you begin to crack the patterns, it's downhill from there.
On the surface, it sounds to me like that is what this guy did. And once he figured the file format, then poking bytes to bump experience or whatever becomes almost trivial.
The caveat being, of course, what kind of protections the AE team put onto the files, such as checksums, byte encoding, or whatever. But, OTOH, that, too, is part of reverse-engineering.