TD1 flags when raised are permanent. It cannot be reset by dealers.

When Dealer connects vehicle to database, if TD1 is positive it is stored permanently attached to your VIN number on VW Groups database in Germany. Doesn't matter if you revert to stock, etc.

But, my thoughts have always been, if I tune and get more performance out of a tune I am voiding all warranty related to that tune anyway. If VW honour any kind of warranty post tune its a bonus.