For resetting character skills and masteries better use programs like GDDefiler or GdStash. What you want in the OP might be hard or even impossible. If you still want to mod, I suggest taking it step by step and start grom Simple mods. Make sure you setup Asset Manager precisely like on this guide [Script][Basics]Modding Beginner's Guide I (1.2.3 Setting Up Asset Manager) and then try to make a mod with one Simple change to make sure it works.