So….you have a kasha about techias hamaysim being a shinui.
It’s not a kasha. It happens once. The rambam is talking about “yemos hamoshiach,” that in the messianic era, he holds that teva will remain. A one time change does not constitute a different world order.
…and “who says he has to be living,” has got to be the most twisted argument on this thread. A dead messiah is a chidush; it’s a given that moshiach will be a redeemer, and thus alive; to say that he can start, die, and come back to finish, is the novel idea which requires a proof. Of which, there isn’t any.
I love how when faced with an explanation of the sources chabad messianics give, you just pivot to “what about this rambam” – it’s like how christian missionaries bombard you with “proofs,” even as you pick one off after another… they’re going they’ll stump you o one, but in reality they’re all nonsense.
Yeshivos have a mesorah. You’re not aware of that mesorah by your own admission; the way American yeshivos learn is largely from rav aharon. The very slow mahalach was popularized by rav leib mahlin. It works, so they do it, even though many gedolim were opposed. In eretz yisroel it’s different.