I think codex decorum doesn't sound right. It doesn't make sense because it translates as book of leaders where as it should really be something like book of guidance or lists of guidance. So maybee Codex Magisterium (an account book of guides/guidance) or Bibliotheca Magisterium (a library of guidance). The verb to guide is actually rego, regere, rexi, rectum but I doubt we want to call the place the rectum so I put in Magisterium meaning directorship , magistracy; direction, guidance. What do you think?

Bibliotheca Magisterium
Codex Magisterium