# RAILS_ROOT/app/helpers/custom_tag_builder.rb
class CustomTagBuilder < ActionView::Helpers::FormBuilder

  def self.create_tagged_field(method_name)
    define_method(method_name) do |label, *args|
      label_name = args.first.blank? ? label : args.first[:label] # my change
      @template.content_tag("p",
        @template.content_tag("label",
          label_name.to_s.humanize, :for => "#{@object_name}_#{label}") +" 
 "+ super)
    end
  end

  field_helpers.each do |name|
    create_tagged_field(name)
  end
end

You can then use this in your views

form_for @your_model, :builder => CustomTagBuilder do |f|
  f.text_field :fullname
  f.text_field :email, :label => "Email (will not be published)"

My change tests for the presence of a label argument otherwise using the name of the form field/model attribute. In this case the fullname attribute will be outputted as “Fullname” while “Email (will not be published)” as the label for the email text field.