"Customizing your Origin in D&D"

[Segev]

Ah, I see the issue. I was reading this through the lens of "AL document appendix", not "Tasha's" and home games, where "rule 0" of DM fiat is assumed to apply.

However, sanctioning it in the book gives the same kind of presumption we were talking about in another thread earlier today: if it's in a core-ish rulebook (Xanathar, Tasha), players will assume it's ok unless the DM warns them in advance.

I think this is one of those things that's "big" enough that most players and DMs experienced enough to know of them will also know to mention them one way or the other.