To the best of my knowledge, no candidate has ever before refused to participate in a debate because he didn't like the moderator. That was the "rule change" I was referencing. Certainly there have been instances before where debate hosts have put moderators on the panel who had personal problems with one or more candidates.
The RNC did boot NBC out of the debate cycle because they didn't like the questions they asked and Trump's action is not all that different. There are precedents for the RNC action however. Trump is, I believe, on new ground.
It will be interesting to see how this plays out if Trump is the candidate. Will Fox News abandon their role as promoter of the Republican candidate? Certainly they won't support Hillary or Sanders but I suppose they could just sit on the sidelines.
I've also heard rumblings that the RNC will not allow Trump to participate in future debates if he shuns this one. I suspect that is an empty threat, however. I think the viewer ratings for this debate will suffer without Trump. Is anybody really interested in watching a debate that doesn't include him?