This is actually a rule in the game; you can change the rules to suit your needs. So, technically, all changes, both potential and actual, "exist" in the rules based on this one.
The Most Important RuleThe rules presented are here to help you breathe life into your characters and the world they explore. While they are designed to make your game easy and exciting, you might find that some of them do not suit the style of play that your gaming group enjoys. Remember that these rules are yours. You can change them to fit your needs. Most Game Masters have a number of “house rules” that they use in their games. The Game Master and players should always discuss any rules changes to make sure that everyone understands how the game will be played. Although the Game Master is the final arbiter of the rules, the Pathfinder RPG is a shared experience, and all of the players should contribute their thoughts when the rules are in doubt.
Yo dawg, I heard you like rules. So I put rules in yo rules so you can follow yo rules while following yo rules.
So you literally cannot come up with a concept that can't be done using existing rules because the rules for such a concept exist as potential rules due to the rule that says you can change the rules to fit your needs. Of course, that brings up the issue as to whether you can change the rule that states you can change the rules. If I can change the rules to fit my needs, that means I can change the rule that states I can change the rules such that I can't change the rules. But then, if I can't change the rules, I can't change that rule. But then, you have to keep in mind that there is an exception to every rule and the exception, here, is that you can't, logically, change the rule that states you can change any rule to its negation because doing so would result in a paradox (argumentum ad absurdum). So what is the exception to the rule that there is an exception to every rule?