1. Remove valve cover.
2. Examine contents.
3. What do you see? Nice engine parts, thin brown film? Piles of black goo?
If you see lots of black goo all over, then maybe it would be advised, but a change of like, using a liter of ATF with the oil change, run for 15 minutes, drain, fill with regular oil and a new filter will work just as well.
If you don't see an ugly problem, no need to do anything. 999 out of 1000 TDIs (or maybe better) will be just fine. If good oil is used, and regular oil changes within recommended service intervals are followed, you will never need to worry about doing engine flushes to get rid of accumulated sludge.
Cheers,
PH