gistfile1.rb

class A
  def something
    puts "something in A"
  end
end

module B
  def self.included(klass)
    klass.send :remove_method, :something
  end
  def something
    puts "something in B"
  end
end

a = A.new
a.something

A.send(:include, B)

a = A.new
a.something

# Displays:
#   something in A
#   something in B

Here I didn't really care about being able to access the old method, but you're right!