My experience and Tip with modding for over ten year? : r/skyrimmods
Contrary to rumors at the time, 1.6.640 did not introduce new quests, fishing mechanics, or Survival Mode tweaks. Those were added in the jump from SE to AE (around 1.6.318). Instead, 1.6.640 was a . skyrim update 1.6.640
After downgrading, set appmanifest_489830.acf (Steam's Skyrim manifest) to Read Only and change its "StateFlags" to "4" (Update paused). Skyrim Update 1
(not through Steam) – should launch without Steam if CC is disabled. New mods starting to require 1