UPDATE: Seem to have found it. For the curious, this appears controlled by characters.gamedatabundle. Search for one of the subrace names and you should find it.
Anyone localized the file/parameters controlling the options in the character creator? For instance, giving all the races the option to choose from all the hair colours. And since pale elves can have beards, it should be possible to add them to wood elves as well, and so on.
I've looked around in global.gamedatabundle and there are a lot of values that seem like they should be affecting this, e.g:
{"Subrace":"Meadow_Human","HairVisualDataPath":"prefabs/hair/male/a_m_hair12.asset","FacialHairVisualDataPath":"","HeadVisualDataPath":"prefabs/heads/m_hum_head01/a_m_hum_head01.asset","HairColor":{"A":1,"R":0.3490196,"G":0.2235294,"B":0.1333333}
{"$type":"Game.GameData.AppearanceVariationSettingsComponent, Assembly-CSharp","SubraceSkinVariationTags":[{"Subrace":"Meadow_Human","VariationString":"HUM"},{"Subrace":"Ocean_Human","VariationString":"HUM"}
So far though, the results are meager. By swapping out the prefabs you can give e.g. a wood elf the preset face of a pale elf, but that disappears as soon as you try to select any of the other head presets.