449: Skill Books for Blunt/Blade Maintenance skills.
450: Possibly add a skill book that increases that permanent modifier you receive on character creation for a certain skill. Raising it only one step from your starting modifier after reading (.25 > .75 modifier, .75 > 1.0 and so on)
450a: I only really hope to see this specifically in the agility tree of skills, because they seem like the skills that would have the most reasonable impact. Having a magazine full of pointers about proper execution and practice does go a long way how well you can progress or train.
451: (Potentially combine with 450) Teaching other people in skill levels you possess for temporary modifier bonuses like the books give. (This would also help teach those illiterate characters )
451a. Do or don't make them stack with the skill book modifiers. If they don't stack give obvious benefits and drawbacks to using either.
(451 for me adds a very interesting way to interact with other players and potentially later NPCs if you don't plan to stick together or work together in the long term.)