terrible.rb

require 'fiddle'

module IAmAHorriblePerson
  def unset flag
    value = _wrap self
    flags = 8.times.map { |i| value[i] }.pack('C8').unpack('Q').first
    [flags & ~flag].pack('Q').unpack('C8').each_with_index { |n,i|value[i] = n }
  end

  def class= k
    value = _wrap self
    [k.object_id<<1].pack('Q').unpack('C8').each_with_index {|n,i|value[i+8]=n}
  end

  def _wrap klass; Fiddle::Pointer.new Fiddle.dlwrap klass; end
  def unfreeze!; unset(1 << 11); end
  def untaint!;  unset(1 << 8); end
end
class Object; include IAmAHorriblePerson; end

x = "asdfasdfasdf".taint
x.freeze
p [x.frozen?, x.tainted?] # => [true, true]
x.unfreeze!
x.untaint!
p [x.frozen?, x.tainted?] # => [false, false]

x = Object.new
p x.class # => Object
x.class = Class.new { def lol; 'lol'; end }
p x.class # => #<Class:0x007fccbb06df80>
p x.lol   # => "lol"