Yes, mods to the black plastic panel are required. (hacksaw)
If you go for the Peugeot feline offering, the end of the standard exhaust is trimmed, the existing exhaust finisher is removed and the plastic panel is trimmed. The new quad finisher is bolted to the rear of the car.
The Ruffer exhaust you have seen the photograph of is, I believe, more of a replacement system, although I would expect equivalent plastics mods to be required.
Remember also that the installation of towing brackets is not possible with the Peugeot version, not sure about Ruffer