well, I'm not gonna say that those ones are im
possible. There is
an outside chance that someone could do it, since all three of those species could use the standard body models. The problem is that the amount of work that would have to go into making the heads is too huge, there's a lot of hex editing guesswork involved, and too many ways for it to get messed up along the way.
I'm not gonna take the time to try it. You could do a search for a tutorial by Miro42, for some insight into adding verticies to head models.
I hope I haven't completely dashed your hopes
. Basically, the easiest aliens to make are near-humans. Most of the time, they just need a re-skin. Sometimes you can re-shape an existing head model, and use Taina's replacer tool method to get it in game. That method will work for simple changes like pointy ears, empty eye sockets, simple
horns (they don't usually look that great), or slightly out of proportion faces.
The most ambitious heads I've tried are cat-like Cathar, Sith species, and they're disasters. I did have some success with a Duros head (Nindo Bahr a character in RoR), cat-like Juhani (see jonathan7's random tinkering thread), and a pair of female Devaronians (also for RoR as PCs; the third one was a failure). So you see, it's still hit-or-miss with alien heads.