Earlier I talked about how successes can tailor actions and power methods can tailor worlds. We can go even further when tailoring any game: We can customize the rules. Pretty much all gamers know this, and most game systems acknowledge this. But, few truly embrace this.
Krendel fully integrates optional rules. Rather than regulating them to a single chapter or appendix, you will typically find them right next to the text they are most relevant to, and there's an index to help you find them too. Krendel Core sports over 50 examples of optional rules, and you have the freedom to create new ones as you desire.
Want the player characters to have more Health? Flip to the section on Health for a couple of suggestions. Similarly, if you are looking for options on how to change up experience points, then you'd look in that section.
Options aren't limited to minor tweaks. For instance, Krendel uses an active defense system by default. By this I mean that a target's skill has no affect on the aggressor's chance of success unless the target spends an action to counter (e.g. dodge, exert will, cancel magic, etc.). But you can flip a switch to change the system over to passive defense, removing automatic counters and instead applying the target's skill as a penalty.
So, how the heck to you keep track of it all? Optional rules are nice and all, but its all too easy to forget what ones you are using or for someone to suddenly try to change a rule. This is where the gamer contract comes into play.
The gamer contract is a document that your group works up at the start. It can be a formalized contract, a page on a campaign website (e.g. Obsidian Portal), or just a list of items on the back of a napkin. No matter the form it takes, its purpose is to memorialize the group's expectations. One of the things you should include in your gamer contract is a list of the optional rules you are using. This way, everyone knows what is going on, and if there is ever any doubt, you can always go back and reference the gamer contract.
If it helps, think of it like a style sheet for a web page. All web pages run on the same basic fundamentals, but you can tweak how one appears and functions by changing its style sheet.