class ActiveRecord::Encryption::Properties

def []=(key, value)

It will raise an +EncryptedContentIntegrity+ if the value exists

Set a value for a given key
def []=(key, value)
  raise Errors::EncryptedContentIntegrity, "Properties can't be overridden: #{key}" if key?(key)
  validate_value_type(value)
  data[key] = value
end