How to disable callback

Rails
1

How do I locally disable a callback from being performed?

My class has

class Keyword < ActiveRecord::Base

after_update :switch_versioned

private
  # Callback used to warn the user that an updated record
  # has not been saved in the version table
  def switch_versioned
    logger.debug "coucou"
    self.versioned= false
  end

But another class has a method that sets

@keyword.versioned= true

so in this case I want to disable the callback… there is probably a
better way to do it?

any help appreciated

Isabelle