i now its a bit to late now cuz iv booked my car in for a cat back stainless, but do i loose warranty on anything due to me haveing my exhaust changed??
Any modification that takes the car away from standard spec could technically void your warranty. I'd say that ones for performance gains will be more likely to, given the extra strain on various parts of the car.
That said, some people here say that they get no problems when making warranty claims and the standard advice seems to be to have a word with the service manager at your local dealer.
I'm no expert but a different exhaust will effect how emissions are cleared from the engine. A change in pressure could occur so in theory they could say the warranty is void on some engine components. Wouldn't void the warranty on wheel bearings for example as it makes absolutely no difference to them.