Depends where you plan on taking a "spin" at. Also, if something happens to the car because of you flashing the Cobb, you can be held liable for the repair costs and here in Germany, it ain't cheap.
If you plan on taking a spin on the 'ring with the rental, it is strictly prohibited and if you are involved in an accident, you are liable for all the damages incurred.
Quote from Ezeedee regarding car mods:
"you're only done when you sell the car