It is possible and very easy to do (figured out how to do these things for myself). However, the issue is that you will have human ears, which elves and tieflings don't have. So it would look weird. Elven faces for tieflings are much better options since they both have pointy ears so it won't look off when you have elven heads for tieflings.
I would share my file, but since the mod isn't originally mine, I can't do it. Here is the tutorial if you wish on how to do those things yourself (hopefully, it is easy to follow):
Edit: Fixed a few grammar mistakes.