with_optionsでスッキリ

after

  with_options if: :new_record? do
    before_validation :initialize_hoge1
    before_validation :initialize_hoge2
  end

  def initialize_hoge1
    hoge1
  end

  def initialize_hoge2
    hoge2
  end

before

  before_validation :initialize_hoge1
  before_validation :initialize_hoge2

  def initialize_hoge1
    hoge1 if new_record?
  end

  def initialize_hoge2
    hoge2 if new_record?
  end

Railsで特定の条件下で走るバリデーションを作りたい - Qiita