http://en.wikipedia.org/wiki/Magnuso...s_Warranty_Act
It can cost you plenty of $$ up front to fight it, but its possible to have BMW prove that the DPs caused a failure.
And you cant have a warranty VOIDED. Warranty claims can be denied however due to aftermarket parts. A lot of the time, dealers and techs will look the other way for simple mods. I had my local dealer tech tell me as long as i didnt inject anything into the car (meth or nitrous oxide) he would be ok with most mods (fmic, DPs, intake, tune). It helps that he is a fellow tuning enthusiast but this is going off what he SAID. If the chips were down, i am not sure what would actually happen with my FMIC, chargepipe and intake if i, say, needed turbo replacement.