code: def update_custom_field_options(custom_field_key, new_options,
        keep_existing_options)
        custom_field_key = CGI.escape(custom_field_key)
        options = { :body => {
          :Options => new_options,
          :KeepExistingOptions => keep_existing_options }.to_json }
        put "customfields/#{custom_field_key}/options", options
      end
docs: Updates the options of a multi-optioned custom field on this list.