reverse programming logic

Has anyone seen, or think they could make a program that would take source code in the language of your choice and attempt to automatically make a reverse version of the program, or something of the sort?

Example:
Original program Inputs: A B
Original program output: C

New program input: B C
New program output: A

How hard do you think it would be to manually alter source code in this manner? Should be easy for the most part right?
How hard do you think it would be to make a program that does it automatically once the input/output combinations are specified?