Which, if I understand it correctly, doesn’t require him to reverse himself. the question in that case doesn’t appear to be whether he wasn’t eligible to be POTUS, but whether they could keep him off the ballot because was ineligible. He ruled, yes if he is ineligible for POTUS, they can keep him off the ballot.
The easy out here is that he rules, like a previous judge ruled, that the amendment doesn’t actually restrict one from being POTUS.
No chance trump doesn’t win a primary election for Republicans, unless they block him from it.