asked about adding custom races. I don't remember the rules for Mountain Folk or Dragon Kings, so I can't answer that directly.
Let's have a look at we're doing instead, so you can form the answer on your own:
Right now, we are exposing more of the internals of a character template. We are doing this to simplify Anathema: What we have shown you so far is actually a side effect, not an end of itself.
So, as long as your new race is just a re-skinned Exalt who mixes and matches existing parts, you're good to go.
However, there will be some parts we do not expose - remember, side effect - so this process won't give you full control over everything.
Mostly though, you will get stuck when you need new behaviour, instead of just new names and number.
Take 2E Alchemicals, for example:
You could create something with Attribute-based Charms, as Lunars had them; define Castes somewhat different from the Lunar Castes; give it free picks; custom Bonus points; enter the various Charms - but you still won't any way to switch Charms or build Arrays.
You'll get to a similar result with 2E Infernals and their second Patron Yozi.