I think it's something like if you have a rule you want to remove, first "catch" that rule from another town. For example, you want to get rid of "Random" in Centra? First play alot of games in Dollet, and then go play cards in Centra. There's a chance that the two Random rules will somehow clash and be removed from that area. I'm not 100% about this.
As for Balamb, there is a man who's fishing in the town who will actually remove the rules for you.
