@ProphetPX - It's not that simple, and in another way it's not complicated either.
Note too, that most of what is in this thread is a decade old and very out of date.
How do you "build" house rules? - with the editor.
You can build your "house rules" the same way as everything else... make up something in the editor and (like TobyFox said earlier) give everything a source, so that when you select that source (or "set" of "rules") what you have developed becomes active - whether it is new feats, skills, or alternate feats/skills, or changes to something existing. Search the forums for individual elements of what you want to do. Some things will be creating a new item, other will be scripts that modify something that already exists.
If you haven't done much with the editor, use it to look at how someone else has already done something and look at the many examples/guides that people have done to assist.
Eg: Hero Lab Help -
Hero Lab FAQ,
Editor Tutorials and Videos,
Editor & Scripting Resources.