Don,
It depends. If you are resident of Denmark and import a car, it has to be registered on Danish licence plates immediately upon importation. As a Danish resident, you are not allowed to drive a single kilometre in Denmark on foreign licence plates. However, if you are moving to Denmark, you have 14 days to change the plates (and pay the registration tax of 180 percent of the value of the car!) Otherwise if your stay in Denmark is temporary, you can upon application keep your foreign licence plates for up to one year.