my car is not a lease, so i am was happy to mod away.
with that said, i have the bms downpipe and recently purchased the arkym quad diffuser with cyba black chrome quad tips.
i do not know how the fitment is with other brand tips or diffusers, but with my combination, i had to cut off the stock tips real close to the muffler, thus removing the exhaust flap (vaccuum line) and welding in some new pipping off the stock muffler to get the cyba tips to fit correctly in the diffuser and sit flush.
the answer to you question in my case is that my vaccuum line had to be cut, which may not be to great having a leased car.
Last edited by badblkX6; 04-24-2012 at 07:19 PM.