Appvars can be edited by any program you make, but you can store any kind of data to appvars. Appvars are just a a chunk of memory that you do whatever you want to. There is no inherent structure, so unless you know the format of the appvar, there is no way of knowing what each byte represents. If you do know the format, you can make an editor to edit the data. For example, I played Donkey Kong (DK5ION) that saved highscores to an appvar. I unarchived it, opened Calcsys, figured out the format of the highscore list, and edited it. I did the same with Graph3D, to edit the Z= equations.