Based on this excellent post by z3n at http://www.twcenter.net/forums/showt...XML-and-the-AI, there is indeed a way to "fix" or at least revert the campaign AI behavior.
1. Navigate to your 2.35a folder and make a backup of descr_campaign_db.xml and descr_campaign_ai_db.xml.
2. Download the previous 2.35 (NOT 2.35a) version and locate that previous version's descr_campaign_db.xml and descr_campaign_ai_db.xml.
3. Replace the current 2.35a's descr_campaign_db.xml and descr_campaign_ai_db.xml with the previous ones.
These changes are most likely NOT save-compatible, so keep the 2.35a descr_campaign_db.xml and descr_campaign_ai_db.xml handy if thing's don't improve. The best way to test if this works is to boot up a Pahlava campaign, disband your entire non-free upkeep army, and buy up AS settlements one by one. If they declare war on you even once before turn 100, then the changes don't work. If the AI goes bonkers and forms an international coalition against Gigantus, the patch didn't work. If the game straight up crashes, need I say more?
However, if the AI now declares war only with nowhere else to expand to, and certain factional relationships return (AS never, and I mean NEVER, declaring war on human Hayastan, Pahlava, or Pergamon), then this fix worked. Do this only if you want 2.35's mellow campaign AI, instead of 2.35a's backstabbing GoT AI.
If time permits, I'll learn this scripting myself and find a way to balance 2.35's AI's rationality with 2.35a's AI's proactiveness