There is no problem... http://www.hotcarparts.de/section/euro2-bmw.html I'm not familiar with the Diesel E34 but for details on the tds I would ask at the German E34 forum www.e34.de (the answer even if you ask in English).
My latest German imported 540i/6 are upgraded to Euro 2 which lowers the road tax in Germany from around 450-500 to less than half, in Sweden it doesn't matter even non Catalyst cars have the same tax (cars from 2002 and older).
Stephan
1995 E34 540iM/6 #410/797
1996 E34 540i/6 LE #768/797
1996 E34 540iM/6 #774/797
Missed:
1995 E34 540i/6 #631/797
1995 E34 540i/6 #736/797
1996 E34 540iM/6 #788/797
1996 E34 540i/6 #794/797