Do [I_SOURCE:EXPERIMENT] actually do something?
I extracted these generated raws:
I cannot find any example of necromancer using this interaction in Legend Viewer. :-(
I cannot find any example of necromancer experimenting on anything in Legend Viewer outside of Experiments(creature) description either. ¯\_(ツ)_/¯
The experiment is the result of it happening, so it worked. There are individual traces in the
victims sentient and nonsentient who had been turned by the necromancer after being captured from a site or around the tower. Possibly more omissions were made from 50. but try 47.xx, when it was first added.
The DF wiki stipulates under [EXPERIMENT_ONLY]:
Disallows use of the interaction in play, but if the interaction animates or resurrects corpses, or has an I_SOURCE:EXPERIMENT tag, it can be used in worldgen. Animation and resurrection interactions do not need I_SOURCE:EXPERIMENT to work in worldgen.
[IT_MANUAL_INPUT:victim] is overall targeting for wg, same as if it was 'creatures' face to face or 'corpses' in regular zombies (I don't know if a halfway of a necro-hybrid that only makes experiments is possible)
As to actually influencing it like to make your own experiments (crafting people into monsters dr moreau style) the science is still being hashed out. You can turn off some experiment types like the infectious ghouls from the advanced worldgen settings. My own theory is that you'd have to substitute custom experiments very carefully while turning the generated ones off, as it relies on a roster of castes (ghoul, animals, soldiers, a giant creature type) because of the method of how they were made exacts from a certain number and quality of victims. Perhaps the same creature titles under different castenames.
Having them in worldgen would be even harder, in part to the tokens that allow a creature to experiment as a night creature being very prone to CTDing when they lead a playable civ.