Even after signing the Republican National Committee's "loyalty oath," Trump has always made clear that his fealty to the GOP was always contingent on being treated fairly by the party. The only problem is that he has claimed for himself the right to define what is fair and what isn't.
If a former New Hampshire Republican chairman had succeeded in getting Trump thrown off the primary ballot, it would have legitimately constituted unfair treatment. (I believe concern that party leaders would interfere with his state ballot access and try to keep him out of the debates were the primary reasons Trump kept the third-party option on the table initially.)
It's true that many of Trump's past statements and some of his current positions contradict the Republican platform, but that's never been a standard candidates have been held to before. John McCain had broken with the platform on taxes, immigration and campaign finance reform prior to becoming the nominee in 2008.