UPDATE 2.1X ADDS NEW FUNCTIONALITY!Send your own fuses and locks trough terminal, talk with chips with broken signature. If you connect terminal Tx pin to PCB Rx pin - manual mode will be enabled automatically. This requires Tx-terminal pin to be HIGH and OUTPUT when idle. It must pull up the 10K pulldown. If this condition is not met, doctor will work in normal - automatic mode.
Can't you work around it in s/w?
The method employed for this was brute force; I had a program fire off one random sequence after another, checking the chip state after each sequence
I think someone mentioned this in passing in another post, probably in the last 12 months.
The Atmel guy I talked to swore up and down that it wasn't possible to change signatures...
I remember them being a logical extension of the commands to read / write the program Flash. I believe I found three references. I know one was on avrfreaks. If you want a hand finding the material just let me know.