You should list school #2 as your NMSC “first choice” even if it’s not truly your kid’s choice. There is no benefit to listing a school that does not provide NMSC scholarships.
(Also: does the 2nd choice school offer EA?)
Yes you can change your “first choice” college up until May 1st.
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On a separate point, since you’ve written:
(boldface added by me)
It’s really your son, and not you, who should be filling all this out. Just saying.