The Wormhole wrote:
I know that episodes like The Vengeance Factor or The Hunted (episodes I was watching when I first thought this up) would still have been the same episodes if they were human colonists rather than seperate races.
The problem with these two episodes in particular is that their premises depended upon someone being medically altered in a way that might seem less plausible to suppose being done to a human.
Now, if you had said The High Ground,
then I would certainly agree, assuming there was a reasonable way to get past the Federation membership issue.
TOS did use actual humans a lot, and it did have very non-humanoid aliens, such as the Horta, the vampire cloud, Medusans, and Yarnek the Excalbian. Yarnek was particularly effective, I thought. The Kelvans were totally non-humanoid but had specifically assumed human form to steal the Enterprise,
which was an effective trope.
TAS was also able to bring non-humanoid aliens to the table, in its own low-tech way.