Psyops essentially seeks to erode (or sustain) the loyalty towards a government. To simulate psychological warfare from the real world within a strategy game like this you could easily get most of it within two dominant components:


1)Propaganda

2)Sabotage


Propaganda is essentially the weaponization of influence. As a measure in the game as an addition to the current bonuses of influence, an enemy's system within my influence area ought to inevitably turn its loyalty over to me given enough turns have passed because of "propaganda effects." Part of the problem I have with influence is I have yet to appreciate it. The difference between a zone with influence and no influence goes by unnoticed, really. It's cool but the usefulness of it needs to be clear. It has to give enough of an edge (or threat) for me to want to develop it or guard against it.


Sabotage works by frustrating enemy productions and weakening their belief in their own strength. This could be represented as a sub-section of manpower which can be sent to an enemy's system and which causes a steadily increasing suppression of that planet's output including FIDSI's and increases unhappiness so the enemy is constantly having to suppress or seduce their own populace (fields catching on fire, ships built on that system tend to explode, money goes missing, people go "missing", tech is stolen, etc). The system could inevitably turn over its loyalty to my Empire given enough time has passed and the saboteurs haven't been stopped.


Also, along with overall Empire strength, where the enemy Empire is riddled with enough saboteurs, I ought to gain diplomacy negotiation bonuses, and these bonuses are furthered by how much of my influence/propaganda covers their territory so that influence and sabotage work together to form the diplomat's weapon. On top of that, sabotage ought to give bonuses to ground battles. In terms of gameplay I want to be able to simply hover over a system and click "sabotage," provided I have the Sabotage tech and sufficient forces to do that. 


Some new techs could be made for propaganda in the "Empire Development" side of the tech tree. It definitely needs to be a more worthwhile aspect of the game. But sabotage should definitely be a new tech under the "Empire Development" side of the tech tree with increasing strengths through the tiers and as an alternative branch of choices to raw military power so that where a military force comes against a diplomacy faction, diplomacy actually has a weapon other than "cease fire" and "create alliance." They have "Propaganda" and "Sabotage." Sounds fucking awesome.


Also it would be cool to see a faction that specialized in psyops, or a minor faction that gives sabotage bonuses, like pirates, or the cultists from Endless Legend?


This guy has some good ideas for counter-measures:

https://www.games2gether.com/endless-space-2/ideas/202-bring-spies-on-endless-space-2

Another weapon of diplomacy - common goals:

https://www.games2gether.com/endless-space-2/ideas/140-goal-driven-diplomacy

Cool ways to add a challenge to influence to make it feel like a playable aspect of the game for diplomacy:

https://www.games2gether.com/endless-space-2/ideas/617-area-of-influence

Another post along these lines:

https://www.games2gether.com/endless-space-2/ideas/596-espionage-in-game