If you mean to read the program off the uCs, then modify the code, and then reprogram it, I doubt it is possible. They would most probably hav used lockbits (or the equivalent) to prevent code memory from being read by an external source once it has been programmed in during production.

You would probably either have to write a whole new program from scratch (yaaghh!!), or introduce your own uC system which can intercept the signals and control the rest of the unit. Either way is a lot more work than being able to modify the original program , but engineering life is rarely that easy :-(

Still, the second method seems pretty do-able

kundi