Welcome. I don't know what the rules are in Portugal. Probably the best place to ask your question would be the US site as the guys there are into major mods. https://www.fitfreak.net/forums/
Here in the UK, it is illegal to fit a shunt, so I doubt anyone has done it unless they race a Jazz.
There are performance /customising enthusiasts who do Decat their cars in the UK. They get round the MOT problem by converting it back to road legal just long enough to pass the test for another year before returning it to how they like it. By refitting the Cat converter, maybe changing outrageously illegal Hi intensity lights to standard ones, fitting a set of legal number plates etc. and of course some are willing to risk driving with no current mot, insurance, road tax etc.
Having a current MOT may reduce their chances of getting 'caught' but the car is still illegal, and in the UK at least it will also void their insurance. No Insurer would allow a modification that makes the car illegal.
So dont try this at home folks.
Mike13 if you are determined to investigate further try googling 'decat' for more information.
The problem with testing is often the exhaust emissions. Whilst it may be common in Portugal to offer a tip /bribe to overlook minor things (unlike in the uk where the system is open to abuse by garages charging for unnecessary repairs) some countries ,such as Bulgaria now minimise corruption /cheating by having the rolling road Brake efficiency tests and emission tests carried out with a live on- line connection to the government authority who also record the result. With a close up shot of the Chassis number and the whole procedure monitored on cctv to ensure the correct car is used for the tests.
