Last time I went I had my ledas, exhaust and sports cat.
The service bloke came out had a look seemed quite interested in the mods asking how they improved the car etc., no mention of them effecting the warrenty.
They did not ask for any servicing records, which I was quite surprised about.
It was for a heater fault but from this blokes attitude I dont think they would have had issues with any other problems.
It is in the garages interest to do warrenty work so voiding a warrenty because of mods is losing them work.