Once there were easy gearboxes where it was enough to withdraw the eprom memory, read it, modify it, and insert again it into its seat.
Since the last years the gearboxes have different kind of memory and in most cases all soldered and so the "modus operandi" changes in this way: unsoldering, reading, modifying and soldering again.
Lots of gearboxes ( if it wasn't enough ) have both soldered memory and stick with glue or resin; so that it could happened once unsoldered and removed the eprom to remove also some of the data transmission tracks.
Repairing and soldering needs great patience and good manpower, and most of all a very good sight.
In spite of all that it would be impossible to have the certainty to have done a good job.
Here the need of a peaceful and clean place, possibly not set in mechanics department full of greasy, oily, dirt and dust.
Obviously this room should be equipped with different kind of welding machines, positioning displays with different enlargements and perhaps with a digital microscope, where the imagine is visible on a screen and could be enlarge 20\25 times.
Logically we have three or four computers, and this is the description of our gearbox room.