sorry for the late reply, but you need to subjugate them. An empire wont ascend if you vassalize it and take steps to keep it weak. should they become independent/be independent/get to powerful as a subject, they will ascend and nothing can be done by that point except banish and annihilate

No worries, appreciate the effort. I was hoping for a less time consuming way, for example a game setting, just to test and see if the issue is actually caused by these two mods. Subjugating 3/4 of the galaxy by end of mid-game can be quite a task, especially when you play huge galaxies with dozens of AI empires.

For anyone who is still trying to do this, you can. You need to do 2 things. Go to the workshop folder for this mod (steamapps/workshop/content/281990/2044599287/common)

First, go to the ascension_perks folder and open up the text file. There are 3 perks, each for the normal, hive and machine races. Find where it says AI weight change Factor = 10 to 0. This will tell the AI that the perk is the lowest priority and they won't pick it.

Second, go back out of common and into the events folder. Find fallen_technologies_events.txt and open it. Use the find tool and locate a portion with the title "# AI Ascends without AP slot". About 10 lines down, where it has "is_ai = yes", change this to no. Currently this event allows AI to ascend without the perk, changing this line means the event won't occur unless it's for a player...I think.

So far I'm in 2500 with like 7 empires who've all got Dark Matter Power and used to ascend, haven't seen them ascend since making these changes.

DO NOTE: If this mod gets updated, these text files get reset so you'll have to reset them each time.

uFuqinwitme's method should work, but it's a much better idea to just do that as a new local sub mod instead of directly changing the ZOFE files. That way you'll never lose it, and can enable/disable at will.