Creating Aliens
It seems you can easily create Aliens for players, or allow them to create their own. Just keep it balanced. +1 to one stat, -1 to another, +1 to one skill, for a -1 to another. I wouldnt allow more than two stats/skills to be adjusted to keep it simple , and avoid min/maxxing. Most players will be happy with just "cosmetic" changes, changes in appearance to make the Alien. You can also just have the Alien based on Humans with no adjustments, just the bizarre appearance. (blue skin and faceted eyes for example) The role-playing will make the alien come alive.