Re: chiptuning GT
Personally I wouldn't want to risk voiding the warranty. They always say remaps can't be detected by the diagnostics software, but any testdrive will and apart from that I know that the diagnositics software can read out how many times you hit the rev limiter, what the maximum number of revs was at any time and so on. I don't know if on the JTD's -like on the petrol versions- the rev limiter is set at a different rev number when you do a remap. But if it is done, it should be easy to detect remapped cars (if you are searching for it).
When your engines failes on you, you probably head to the dealer first before you consider to let the tuning company undo the remap. So in real life undoing the remap is probably just a hypothetical option.
Just my 2p.