When my D23 made her college decision, many of the schools she turned down sent her auto-messages wishing her luck and indicating that as a previously accepted student, she would have a better chance at admission than the typical transfer student if she changed her mind later. She hasn’t changed her mind, but it was reassuring to know that (though, yes, she would not have had any of her original merit offers had she transferred). So your kid might have a decent shot.
However – I recommend giving it time. An initial burst of enthusiasm followed by a letdown as reality sets in and the real work begins is very typical among freshmen. In fact, it’s probably more typical than total contentment with one’s college choice. So he’s having a normal experience of settling in. Classes first semester are an adjustment process (and these rarely end up being a student’s favorite classes, because first-semester students have the fewest options), and friend groups shift around as people find each other gradually. It can take 2-3 semesters to really feel comfortable. I would keep the usual transfer application deadline (usually in March) open as a possibility, but don’t rush it. There’s no guarantee he’ll love the other school more or have an easier if/when he gets there, so in the meantime, he should look for opportunities to find his bearings at this one. Seek out professors for advice, maybe take advantage of on-campus mental health services, try out school clubs, sample the local (arts? music? restaurant? sports?) scene. It does take effort. Focus on that, and even if he does apply to transfer to the other school, he may find by the end of this year that he doesn’t want to.