It is possible to bypass the slow down warning system in some cars. But should you do it? Well that depends. Generally the answer is a definite no, but if there are no catalytic converters installed the system is redundant.

My car still has catalytic converters...

If you have catalytic converters it is critical you keep the slow down warning system operating to protect your investment. With a bypassed slow down warning system there is no way to know if a problem is causing an overheating condition. And no, the early generation Bosch engine management is not always smart enough to detect Ferrari misfires that can cause cat overheating unlike a lot of other modern vehicles.  

My car has test pipes and catalysts removed....

Your car is a candidate for slow down system bypass, but there is a set of other problems you may encounter.

1) It's illegal. In many countries and states there are emissions testing schemes in place. To abide by the law it is recommended to keep the exhaust system in operating within factory spec. Some jurisdictions do not test for emissions, however it is likely that removing the catalytic converters is still an offence.  Keep in mind the risk of a mechanically minded inquisitive police officer, and if you haven't disclosed to your insurer you may discover problems should the worst happen. Also, in this age of climate change and increasing health awareness it's just not cool to pump those nasties into the atmosphere for others to breathe. If performance and free flowing exhausts are important to you there are plenty of after market high flow catalyst options out there that provide the best of both worlds, cleaner exhaust gasses along with unimpeded flow.

2) Check engine lights. While you may have resolved the temperature measurement and slow down light issues, most cars after 1996 have O2 sensors before and after the catalysts. The up stream sensor monitors raw exhaust gas and adjusts engine tune accordingly while the downstream sensor detects catalyst efficiency and if it detects no change in gas composition it generates a check engine light. This is an instant fail at emissions testing time, and poses a risk to the cars value to an educated purchaser. Bypassing the slow down circuitry does nothing to solve check engine lights relating to inefficient cats.

3) Check engine light version 2. Later cars progressively get smarter and smarter at detecting a slow down light bypass. While early cars were happy with a constant dummy signal to fool the system, later cars (seemingly 575 / 360 and up but it's not 100% certain) expect to see a changing temperature within the cat with time relating to engine coolant temperature. If the cat isn't up to temperature in time a check engine light is triggered. 

Easier models to bypass

If you have a Ferrari F355 with motronic 2.7 the job is easier. Motronic 2.7 was a more simple system with O2 sensors only before the catalytic converter, so the cats could be removed easily without impacting the engine fuel mix ECU operation. To bypass the system, add test pipes to the exhaust and install two bypass dummy loads to the slow down circuit connector. The thermocouples and CCU's can then be discarded.

348 models have mixed systems. Earlier models can simply have the CCU unplugged (only if cats have been removed!) while later models are closer to the early F355 models and will generate an error if the CCU is unplugged. Unfortunately 348 CCU replacements from the factory are a huge cost so watch this space for a Technistrada redesigned option for 348 owners.