Apologies if this is obvious with the game installed, but I'm at work...
I'm most interested in messing with the AI. Nothing I've seen online says it's possible for users to directly mod the AI, but there's heaps of developer tweakage and Metaverse "evolved" AI trading.
Can we mod AI?
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(I want to add - I know, it's embarassing to use scripts, but... - a simple script for the AI to detect that it's blockaded. If there's an enemy fleet of X firepower within Y distance, stop building suicidal non-combatants over and over. Well ok, maybe try one or two to see if they get out if that's what the build priorities want, but stop after a failure or two and make some combat ships.
Blockading the AI is easier than it should be, especially when their tech and economy is better than the player's but they've lost to a bit of a rush. A human would realise that they could whittle the blockade down by building damaging ships. The AI seems to get stuck on its normal build priorities which leaves it building constructors or troopships over and over while my paltry survivors from the earlier fleet battles can sit and blockade forever.
So check for blockade: no friendly ships in orbit, damaging enemy close by, last ship to be built got slaughtered. If blockaded, try ship design X (tending to try whatever has the current highest success rate, which'll probably be a big bruiser, but also giving a chance to a small/cheap/all-weapon design, and a chance for a new design as per whatever the present system is). Did it do damage? Yes: build more. No: try something else. If there are non-blockaded planets in empire, cease production at the blockaded port if a couple of builds there fail, until the blockade is lifted. If everything is blockaded, go for broke).