You could make a separate Tech Tree with techs created specifically for your new race, Vidszhite. Might be a bit harder than we'd like it to be, but it's doable without needing to give an OP tech.
Oh, I did. I had reasons to do that anyway. The problem is, the game handles extreme worlds in a very strange way that makes it impossible to do what I'm trying to do without over-writing the entire planet traits file.
1) To colonize tier 1 worlds, each t1 extreme planet looks to see if you have at least one of the "CanColonizeExtremeWorlds" stat. This means if you can colonize one, you can colonize them all, and once you can, getting more than one of this stat does nothing.
2) To colonize Tier 2 worlds, the Toxic and Radioactive worlds both look to see if you have unlocked the Atmospheric Cleansing tech. This means you can't naturally unlock the ability to colonize just one of these two worlds, it's either both or neither.
3) Every extreme planet operates at -50% production by default. To normalize production, each individual planet's trait definition checks to see if you have unlocked its associated Mastery tech, and then they check to see if you've unlocked the Ultimate Adaptability tech. Mastery techs are Specializations, so you can't unlock more than one per tier on your own, and you can't write one tech that unlocks multiple other techs. If you have Ultimate Adaptability, it gives you all the bonuses you'd get from having each planet's Mastery, plus a 25% bonus to Production. Unfortunately, since all the planets look for Ultimate Adaptability, unlocking it for one unlocks it for all.
To do what I want to do, which is give my race a tech that grants them Mastery of all tier 1 worlds, but only allowing them to colonize Toxic worlds and not Radioactive, I have to modify each default extreme world so that it looks for my race's unique technology, which is easy, but forces me to use a mod that over-writes the entire PlanetTraitDefs.xml. AKA the Total Conversion method. I COULD give them mastery of all tier 1s and Toxic by giving my race all the Tier 1/Toxic Mastery specializations at the start of each game, which is also easy, but I still can't give them the ability to colonize Toxic worlds unless I also give them the ability to colonize Radioactive worlds.
This ALSO means you can't mod in new kinds of extreme worlds unless you want them to be Tier 1, and once you unlock the ability to colonize them, they can't be -50% production, because no race would be able to unlock the tech that grants you Mastery of that world unless you want to also modify all of the default tech trees. Still, I guess you could make "Tier 0.5" extreme worlds with the current system, but the other problems are still present.
Sadly, this problem is going to be here a while -- if each extreme world had its own stat, I could do what I'm trying to do with the Append method, but you can't add new Stats to the game, since you can't add Schema or Enums via modding. Each stat is required to be enumerated, or the game will crash, and all enumerations are hard-coded. Can't add Enums via modding. I've tried, and when I asked for help, Kryo told me it's not possible.