gistfile1.rb

task :production_deploy do
  xpaths = {
    :debug => "//compiler/debug",
    :debug_define => "//compiler/define[name='CONFIG::debug']"
  }

  # read config xml and set to production mode, storing old values
  xml = Nokogiri::XML File.open("src/Main-config.xml")
  debug_node = xml.at_xpath xpaths[:debug]
  debug_define_node = xml.at_xpath xpaths[:debug_define_node]

  old_values = {
    :debug => debug_node.content,
    :debug_define => debug_define_node.content
  }

  debug_node.content = "false"
  debug_define_node.content = "false"
  File.open("src/Main-config.xml", "w") {|f| f.write xml.to_xml}

  # do the compile/deploy
  Rake::Task["deploy"].invoke

  # restore old values
  debug_node.content = old_values[:debug]
  debug_define_node.content = old_values[:debug_define_node]
  File.open("src/Main-config.xml", "w") {|f| f.write xml.to_xml}
end

Yeah, there is no xpaths[:debug_define_node], so that was all me.