I don't know how many were on New Hampshire's primary ballot this year, but in past primaries, there are often over 100 people on the ballot running for president, since it is easy to get on NH ballot. You pay a $1,000 filing fee and your name shows up on the ballot. I just googled this and in NH primary, there were 30 names on the republican ballot and 28 on the democrat ballot.
So the RNC would have to allow David duke to run for president as a pub if he wanted to? Not doubting you but it does seem odd that anyone can run under their banner.