German police can be a bit picky as well. German laws on vehicle modifications are the most stringent in europe. Doesn't mean they necessarily apply to you on a foreign reg'd bike though.
Memorise these key phrases:
1) It was like that when I bought it, officer!
2) I thought that was standard spec!
3) Oh, I didn't realise it was a problem here, it's perfectly legal in the UK!*
*replace UK with home country if different
The worst ratbike I got away with riding in Europe, with two different homemade, loud, and highly illegal exhausts
Honestly, you don't have too much to worry about with a foreign number plate. Obeying construction+use type laws in other EU countrys is a grey area, and the police generally stay away from it to save themselves the bother. Speeding and other traffic offences are obviously fair game though!