I was able to get it done at the store at 555 Broadway. It's amazing how simple the process was once the guy agreed to do it (initially he told me they had eSIMs but couldn't sell them - I left the store, and he then came outside and said he can do it).
1 phone, 2 operators. Pretty cool.
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My husband had to show them macrumors page that had step by step instructions on how to do it. Because we were adding 2 lines, they were more willing to help.