When I try to run this I get error: this mod requires a different version of the game.
It does not let me toggle it on. the client is 0.96a-RC8.
That's a safety feature of the game. Just edit the modinfo file's required game version, it just takes notepad.
To be even more clear, this file can be found here: ...\Starsector\mods\AdjustableSkillThresholds\mod_info.json
Even though it is a .json, you can open it using notepad (Though I prefer Notepad++). Got to the line with "gameVersion" and change its value to "0.96a". In this instance, it is line 7. In the launcher, this will cause it to be highlighted yellow, but it will still be activatable. If that bothers you, simply change it to whatever the current version of the game is, instead of 0.96a.
Again, all this does is allow the game to attempt to run the mod. It changes nothing about its underlying compatibility; if some future update of the game borks the mod, this method won't fix it!