I'd recommend to use only the "COST" attribute for all techs and not differentiate between Eden and Plymouth.
Excuse me, what? That is terrible advice. Why would you even do that?! You'll break so many parts of the techtree by doing that.
I don't know everything about techtrees. Most of what I say about them are guesses. Its somewhat trial-and-error. I should have mentioned that in my other post. Nontheless, I see no other way to make this work (if you do, you should tell him). The idea just needs some more elaboration.
I guess that the game uses a tech's id to determine which new units can be built after researching the tech. If that is true, it is probably a good idea to not remove any of the original tech-ids. For example, you'd have to leave both "Robot-Assist Mechanic" entries there, change the cost of one to whatever and the cost of the other to 0 and change requirement of the second to the first.
Again, there is the possibility that all of this is nonsense. And by the way, I never said that it can at all be turned into a working mission. Its after all a weird hack.