Since there are two different metals involved, a little heat applied to the nut will cause the nut to expand at a different rate than what the emblem stud does. it should come loose. One of those little cordless 1/4" hex drive impact tools work small wonders for stuff like this too. Try both.
If you don't have one of those cordless impact tools, you need to get one. You won't know how you ever lived without one.
Carl
