Comment by cryptonector

TFA is all about how to make changes where you drop elements of an enum, and how hard that is. The obvious thing though is not covered: don't do that! Instead you should:

  a. Add CHECK() constraints on columns of
     the relevant ENUM type checking that
     the value is one of the "live" values.
  b. RENAME "dead" ENUM values to indicate
     that they're dead.
  c. UPDATE ... SET column_of_that_enum_type = ...
     WHERE column_of_that_enum_type IN (dead_values_here) ...

(c) can be done slowly, say, with a LIMIT clause to keep load and disruptions down. Yeah, you might have "broken" data for a while, but you can make your queries report better values for columns of that ENUM type in the same way that the UPDATE would fix them.