[Edman951]

I don't think the 535 will fit a 550.

The 535 has 60mm piping, http://www.realoem.com/bmw/showparts...61&hg=18&fg=20

The 550 has 70mm piping.
http://www.realoem.com/bmw/showparts...10&hg=18&fg=20

Considering the Megan is a clamp-on or weld-on, so its most likely 60mm piping.

So you would need to an adaptor to go from 70mm down to 60mm.
Making it more restrictive them the factory muffler.