It is possible to get a reprogrammer that is external and without NASA.
Some Diesel tuning kits fit between the ECU and the injectors and intercept the signal from the former to the latter to change the fueling and timing. They can be removed and moved from car to car. The one I fancy for my (unbought) C1
is such a kit.
This, however, looks like the ebay resistor again.
I'd love one for my 72 MGB GT though.