I don't consider new classes (created by the group), new feats, spells, magic items and monsters as house rules - usually because I actually publish those rules in my Kaidan material for Rite Publishing. We do test these new options with the group, especially in encounters that the opposition get these options to try out. Until they are published, we don't consider them part of our Core rules. Once published, then we decide as a group if they are acceptable or not. Of course this new content is written in the logical (without holes) method we'd apply to any rule.