score:2
In the strictest sense: Yes, that works1.
(But you should be well-prepared for a discussion with the police, just in case)
Since you mention going to Freiburg, we're talking specifically about Germany, and the relevant applicable laws are Β§20 FZV and Β§3/13 KraftStG.
The first one states that it is legal to temporarily use a foreign car with a valid foreign registration. The second one exempts you from having to pay tax.
There are several important preconditions to fulfill:
For example, depending on whom you encounter, they can be very inventive for giving out fines on purely imaginary regulations, such as when your first aid kit has no expiry date or the date is expired (there's no law requiring that), or if you drive with perfectly legal daylight ilumination, which the particular police man doesn't recognize as such.