Pan-Jewish changes to Halakha (orthodox law) are still theoretically possible. The last significant such occurrence was the ban on polygamy in Judaism about a m

Pan-Jewish changes to Halakha (orthodox law) are still theoretically possible. The last significant such occurrence was the ban on polygamy in Judaism about a millennium ago. It's just a question of how many rabbis, across how many streams of Judaism, would need to reach a consensus, in order for it to be reasonable to consider an amendment as "widely accepted". In terms of changing the calendar rules, I doubt that there would be any chance of pan-Jewish consensus for quite a few more millennia, that is, not until the dates of major festivals get significantly more out of whack than they are now.