This will lead to confusion in diagnosis of a "CAT".
Mikes suggestion to give the car a hard drive is nothing to do with fuel adaptations.
Cheap re-manufactured catalytic converter's do not function correctly until the "CAT" as reached its "lite off point". These CATS seem to need long periods of high exhaust gas temperatures before they start to function some still refuse to work, which is probable the Fault with Dave's "CAT"
One of the catalytic converter's biggest shortcomings is that it only works at a fairly high temperature. When you start your car cold, the catalytic converter does almost nothing to reduce the pollution in your exhaust. This is an important note when taking your car for its MOT - make sure that it has had a good steady run to heat up the Cats to working temperature or you could fail your emissions test.
One simple solution to this problem is to move the catalytic converter closer to the engine. This means that hotter exhaust gases reach the converter and it heats up faster, but this may also reduce the life of the converter by exposing it to extremely high temperatures.
Another solution to the problem is fitting secondary air systems, but as still car is not fitted with this system its not relevant.
Also the Car in question will have Magneti-Marelli 1AP EMS , so just disconnecting the ECU would clear any learned STFT and LTFT as this ECU as a voltage volatile memory.