The German speaking world operates a nasty variant of the MOT called TUV or it's Austrian/Swiss equivalent. This is the basis for the anti-tampering legislation the EU is trying to bring in Europe wide (OT, there is a Downing Street petition against this, please sign). Basically you can't modify your own bike exhaust even if you are the chief designer and noise control expert at the biggest bike exhaust maker in the world. There are only three options open to you:
1. Buy an exhaust that comes with a certificate from when the manufacturer jumped through their hoops. Buy anything from Hein Gericke and the efficient types that package it will send you the TUV certificate. Ask Scorpion for this, if they sell in Germany they have it.
2. Having made your exhaust, take the bike to a TUV test station, pay the fees and jump through the beauracratic hoops until they write you the equivalent of a Single Vehicle Approval certificate.
3. Emigrate to somewhere where you don't need written permission rubber stamped in triplicate from a government department to pass gas through a tube.
For a visitor there is one final option. Tell plod to **** off. Switzerland is a signatory to the UN charter. A visiting UK bike only has to meet UK legal requirements. Your road legal exhaust is legal in Switzerland and you don't need any additional documents to prove it. (ditto towing a trailer in Spain and having a sidecar on the left in Austria). The UK doesn't MOT Swiss bikes, so the Swiss plod can't do UK bikes that would pass (if your bike would be an MOT failure you'd be in trouble just the same). They can turn you back at the border as "undesirable" but once you're in you're OK. Unfortunately, uniformed thugs with machine pistols don't often take kindly to such legal advice, so getting the TUV papers to sooth their sense of tidiness is probably easier.