Doable:
"Beyond The Farthest Star" - Depicting an alien as green light wouldn’t have been much of a challenge for TOS. The greater challenge would be in depicting the distinctly alien interiors of the giant alien ship—not impossible given time and money, but challenging. Depicting a non-humanoid being on a viewscreen would have been similar to depicting a Melkot or a Tholian so no big problem there. More time and money to create a model of the massive alien ship, but if you can do a Fesarius or a Doomsday Machine then it’s doable. Life-supoort belts become space suits or drop them altogether.
"Yesteryear" – The biggest rethink here is the depiction of a sehlat and a llematya. The avian historian could be dropped or reimagined into something less exotic.
"One Of Our Planets Is Missing" – This would be pretty straightforward considering how similar it is conceptually to “The Immunity Syndrome.”
"The Lorelei Signal" – No great challenge here.
"The Survivor" – Rethink the Vendorian (and his bit about becoming a deflector shield) and it’s a done deal.
"The Infinite Vulcan" – Drop the 50ft. clones and rethink the Phylosians into something less exotic and it’s done.
"The Magicks Of Megas-Tu" – Lucius could be reconceived into something remotely resembling Satan without being half man/half goat.
"The Time Trap" – The graveyard of ships could be a matte painting.
"Slaver Weapon" – Rethink the Kzinti, swap in the Class F shuttlecraft and set the story on an icy (or at least cold) world yet maybe not even needing environmental suits.
"Pirates Of Orion" – All you need is a model of the freighter Huron.
"Albatross" – Some matte paintings and reimagine the Dramians. A good story giving us some neat McCoy background.
Problematic:
"Mudd's Passion" – While I have little interest in seeing Harry Mudd again the main sticking point are the dinosaur sized creatures. Reimagine those and it you might make this work.
"The Ambergris Element" – I don’t see how TOS could have done this. The appearance of the Argoans isn’t the big problem, but so much of the action takes place underwater and then there’s also a giant sea snake.
"Eye Of The Beholder" - This isn’t much different from “The Cage” except it has non-humanoid aliens as the zoo keepers. Curiously the Talosians in "The Cage" were initially supposed to be non-humanoid. In this case remaking the aliens into something more humanoid undermines a lot of this story.
"The Jihad" – A fun story, but all the aliens would have to be reconsidered. The ever changing landscapes would also be challenging unless completely rethought.
"How Sharper Than A Serpent's Tooth" – Basically a retelling of “Who Mourns For Adonais?” but with a very different alien god creature.
"BEM" – The essentials of the story are okay (they did essentially this in TNG’s “Justice”), but depicting multiples of lizard beings as well as a colony being (Bem) would have been impossible. It would have to be totally rethough such as TNG did.
Wouldn't bother:
"More Tribbles, More Troubles" – Cyrano Jones and tribbles again? What’s the point?
"Once Upon A Planet" – Not a bad story, but we already have “Shore Leave” so what’s the point?”
"The Practical Joker" – Not a reall challenge to do, but I always found this episode stupid. The holographic rec room would also be a challenge if not rethought.
"The Terratin Incident" – Shrinking the entire crew visually would have been very challengin if at all possible.
"The Counter-Clock Incident" - Neat to see Robert and Sarah April, but aging the crew backwards? Forget it.
