test.rb

module SomeMethodsPlease
    def self.included(klass)
        klass.instance_eval do
            alias_method :old_initialize, :initialize
            def initialize
                p "the new one"
                old_initialize
            end
        end
    end
end

class SomeTestingPlease
    def initialize
        p "the old one"
    end
    
    include SomeMethodsPlease
end

SomeTestingPlease.new

# => "the old one"