Action RPG Inventory System

I have a few questions regarding this inventory system if anyone has an information related, appreciate it:

  1. How big of an architectural shift is required to make it server authoritative to prevent cheating?
  2. Would major portions of it have to be re-wired & re-written to support #1, or can the server functions, multi-casts, replications and event binds be modified / inserted without a total overhaul?
  3. Has anyone else already made progress on this front? (server authoritative inventory)

thanks!