How to change the Special Rules in a Region - FF8 Guide
For the purposes of this example, I am going to be trying to abolish some of the rules in Trabia, the same place where you get Selphie's Card. In particular I want to abolish the Random rule but getting rid of any rule that sucks is good too. The rules that my Trabia has are currently shown in the screenshot above. My next step is going to be going to anywhere else in the world with a set of Special Rules that are different and aren't as terrible as these.
Since I was just in Trabia to check the rules shown above, I am currently carrying the Trabia rules. I'm choosing to go to Timber which (for me) has one different rule, Same. Once I get to Timber I need to challenge the guard repeatedly until he stops asking to mix rules, if you accept when he asks to mix rules then it's highly likely you'll change a rule in this region.
Once the office stops asking me to mix rules I accept his challenge to a game of cards and exit out at the rule screen (pictured below). Now I am carrying the Galbadia rules. That's how simple switching which rules you're currently using is.
I'm going to return to Trabia Garden and SAVE before going inside. Then I'm going to challenge someone to a game of cards and make sure they ask me to mix rules, and accept. When I quit at the rules screen there is a random chance that one of the different rules I am currently carrying (Same) can spread throughout the region or one of the rules in the region is abolished.
What happens is mostly random with a few exceptions. Open has the highest chance of spreading to a new region (25%) over anything else happening. Every other rule has a (12.5%) chance of being selected to either spread or be abolished. This is why it's so important that you save before doing anything - because it's more likely you'll get an outcome that's not preferable.
If the outcome you want doesn't happen then close out the game and boot it back up, load your save file and try again. In my experience soft resets don't work since the NPC no longer asks you to mix rules. You have to do a hard reset.
Note: On the Ps1 version a soft reset is holding Start, Select and the bumper buttons. On the Steam version a soft reset is holding Ctrl + R. A hard reset on both is closing out the game and booting it back up.
As stated previously, what happens after you play a game of cards is completely random, I saved and reset a few times to show you the different results. It took me 3 attempts to abolish random, before I got what I wanted Sunden Death and Elemental were abolished instead.
That's really all there is changing Special Rules in a region. You can return to Timber to pick up that ruleset then come right back to Trabia to abolish some more rules if that's what you want to do. Just remember to save every time before attempting to abolish any rules as it's more likely you'll get an outcome you do not want.