He made himself a public figure now.
Yes. He was able to prevail in his prior lawsuits because he wasn't a public figure. Having appeared at the convention, he has lost that protection. He can't sue over silly, childish name calling.
All of his previously filed suits filed can still proceed, however, and I hope they continue to pursue the media scum that slandered him, including ABC News, CBS News, the New York Times, Gannett and Rolling Stone. A longer list here.