Ruby: Changing the method of another class

gistfile1.rb

module MyModule
  class Client
    def showmetheurl
      puts secret_url
    end

    private

      def secret_url
        'http://www.changethis.de'
      end
  end
end

def change_secret_url(klass, url)
  klass.class_eval do
    private
    define_method :secret_url do
      url
    end
  end
end

change_secret_url(MyModule::Client, 'http://www.isthisworking.de')

MyModule::Client.new.showmetheurl # => http://www.google.de
MyModule::Client.method_defined?(:secret_url) # => true