The only way that a spouse may be added for a lower charge is for a vehicle owned by one partner before marriage.
This then costs only 2.50 €.
A valid CT (not one less than 6 months old, as for a normal transfer) is required if the car is over 4 years old.
On some great and glorious day the plain folks of the land will reach their heart's desire at last, and the White House will be adorned by a downright moron.
H. L. Mencken 1880 - 1956
Some may not like his views, but what a prediction!