BMW will sitll "service" your car. They just wont PAY for any warranty issues. (To be more accurate, they will not cover any warranty claims relating to the engine or drivetrain.)
So they will do maintenance. And if the engine blows up they will 'service' it. But you will pay, not BMW
(Your terminolgy is a bit odd. FWIW... "servicing"... BMW dealers charge $150-220 an hour. NONE will refuse your buisness for a tune. They are happy to take your money,)
Catastrophic engine failures can be expensive. You could just be unlucky, and have a major issue totally unrelated to the tune- but BMW can say "we believe the tune caused the failure"... and short of you spending $100k to go to court, thats that.
Even minor issues and be thousands of dollars.
BMWNA has been know to pay bonuses to techs that ID cars with modifications... it gets tagged to the VIN. Changing dealers doesnt help.
So.... either decide you are a baller and can pay if anything fails...or wait until the warranty is up (or at least wait a few years to make sure you have a decent copy)