To preface this I have no idea how difficult these would be to implement. The purpose behind this suggestion is to make specialist crafters and omnicrafters more viable. Words between * signs represent variables.

3 types of items:
Fundamental Principles of Desynthsis: increases maximum total desynthsis levels by *max single class desythesis level*
A *Level* *Classes* Principles/Manual of Desynthsis: This would count as some amount of successful desynths of a certain level when consumed.
A *Level* study of *Classes* Techniques: Grants *skill* from *class*.

The Fundamentals book and Techniques book would be high level alchemy recipes. The desynth xp book and the technique book would have appropriate extra requirements: class level of X or equipped skill of Y, desynth level of Z.