Imaro
Legend
Sure, that's fine. But it is then important to remember that how many months it took to do the work is not relevant to the players, when they didn't ask you to do that work.
Let us look again at how this thread and question was framed:
"I offered up a campaign, and this jamoke doesn't want to play it exactly as I want it! Who should give in?"
I reject the implicit question of dominance present in the initial framing of the scenario. Instead, I note that the situation in the scenario exists because the creation process didn't start with the players in mind.
Now, if you happen to have the happy situation of having a large pool of players to draw from, that may still work out for you, and that's cool. But that doesn't justify the implicit affront some of these threads have shown at a player asking for a variation. That comes off like some cooks I know who gasp and flutter their hands when a diner asks for table salt. "That dish is as I intended it!" they cry, "How dare they ask for a modification!"
RPGs are, ultimately, a collaborative endeavor. If you put off that collaboration, you're setting yourself up for friction late in the process, where it is harder to adapt.
If we accept that it's a collaborative endeavor at what point do you feel the player should modify their own expectations around character creation to better accommodate a DM's campaign/adventure/game concept? What I see in this example is a single player who wants to play something that, at least insofar as the DM described his campaign concept... at the very least grates against the theme of a GoT-esque style game and could actually subvert them. One of the things that makes the non-human in GoT so terrifying is the mystique and lack of knowledge around them... Once a player can play a Child of the Forest, Walker, Valyrian, etc. that goes out the window. Moreso it also opens up the window for other players to make such requests as why should only one player get to play a non-human?
EDIT: Also I see alot of answers revolving around what the group wants and in this example it seems all of the group except this one player are ok with the parameters of the campaign... wouldn't that be an argument for that single player to adjust in order for the group to enjoy the campaign premise everyone else has agreed to play?