House rules are small fan created additions and replacements to core rules in a rules set. In most cases, they are not officially sanctioned by the designer, in contrast to optional rules. For substantial new material and rules subsystems, use the [homebrew] tag instead.
I've been using a house rule for a while now. If you have a trained skill, and you are making a knowledge check it's free. For example, if you are trained in nature, and fighting natural beasts; you ...