First of all: great mod! This and the one about religions, man those are probably the 2 best mods in my kit (can't wait to see them finished).

Anyway, about the bug. After activating the Nyblax cube and asking it to "make them believe" Stellaris stopped responding. I imagine the effect of my option iterates through every pop in the galaxy and forces them to assume a Spiritualist ethic. If that's the case, maybe you should divide the work by setting country flags then calling an event for every country (but taking one by one and removing the flag only when the work is done) to change its pops, maybe even using a while clause to avoid it running for too long, and keep calling that event from within itself (or with some helper events in the pipeline) with a days delay.