I've not tried to give the player a different race, but I saw comments on discord about non-human players reverting to human.
The Old Realms mod appear to have tackled this by recoding Character Creation. They add an attribute VampireBodyOverride as you can see in their github
This is the offical repository of the Old Realms mod for Mount and blade 2. Feel free to explore the repository, it is publically available. Note that you can't run the Mod without having the n...
github.com
You'd need to investigate their source code it detail to understand how it works. I haven't learnt C# yet.