The top section of the rules file contains global variables, which will have massive effects on the way Civilization II plays. For example, lowering the amount of food each person eats per turn to one will allow massive cities to exist, and lessen the urgency of dealing with unhappy citizens. I also changed the tech paradigm to 15. I put in zero. OK, so I like being a ruthless dictator, so sue me.
Democracies are just too whiny.
The next section lists all the techs and their interrelationships. While you can tinker with all the details here, be careful in the way you tweak anything having to do with how the AI will see things. You can radically affect the game and thus create silly results. There are also three tech slots open for your use. Entries here will not display properly in the game, but they will activate properly, so you'll just have to remember that your new tech of Clown Makeup requires Feudalism and Diplomacy, is required for Combined Arms and gives you the nuclear pie launcher unit.