Warranty claims...thats a nice topic!!
Dealers might baulk at first & you might get the run around between the dealer & the UK importer....
However, its down to "causation"...they have to prove that when you fitted your aftermarket part it caused their factory part to fail. The infotainment systems cannot fail just because you fitted an aftermarket spoiler or alloys. Aftermarket speakers could cause the infotainment systems to fail, & OEM bearings might fail due to aftermarket alloys..
There is the "problem" of retro-fitting OEM parts built for the car, but not fitted to UK cars. In a legal sense, if its fitted as per their workbooks, & the parts are designed for the car, they have no leg to stand on. There is no difference between fitting an OEM skid tray to a UK or a German spec'd car. They are out of the same factory, & the engine design, cooling etc takes everything & all combinations into account.. So long as the PR codes are followed..ie if part "A" is fitted then its wise to also fit the other parts for the PR code...but thats down to fitting it to factory spec/car design spec...
A Judge would chuck out a case where they totally ignore "causation"...