Yes. Adding it as an additional head rather than simply overriding an existing head. It requires new rows in appearance.2da, heads.2da, and portraits.2da, plus a uniquely named head model (and textures, which is obviously the primary goal in this case).
Possibly compatibility issues, especially for more popular heads (like Mullet Man). While it takes some initial setup the first, a custom head is pretty easy to knock out once you've done it once or twice.
You can do this by editing the save with KSE and changing to whatever appearance you want (including the other sex or non-player races).