NO
Your response prompted me to do a wee bit of research, since I asked this question before. xo said it was an open primary. Actually, NC practices a modified open primary in which Independents can vote in either primary.
The reason I wondered about this in the first place was because it seemed odd to me that Nifong held back on going public on this case for at least two weeks, then he went full throttle. I speculated he did this because he didn't want Republicans to re-register as Dems to vote him out for this lynching he has undertaken. I wondered if there was a cut-off date for registering a party change around the time prior to Nifong going public about the case.