Part 2: creating a skill from existing
From Divinity Engine Wiki
This article describes how to create a new skill based on an existing skill. To create a skill from scratch, see My first: Skill. If you have already created a skill, but don't know how to use it, see creating a skill book.
Introduction
Creating a new skill based on an existing skill is by far the easiest, quickest and most utilized method of creating a new skill.