Maybe/app/models/rule/action_executor/set_transaction_merchant.rb

class Rule::ActionExecutor::SetTransactionMerchant < Rule::ActionExecutor
  def type
    "select"
  end

  def options
    family.merchants.pluck(:name, :id)
  end

  def execute(transaction_scope, value: nil, ignore_attribute_locks: false)
    merchant = family.merchants.find_by_id(value)
    return unless merchant

    scope = transaction_scope
    unless ignore_attribute_locks
      scope = scope.enrichable(:merchant_id)
    end

    scope.each do |txn|
      Rule.transaction do
        txn.log_enrichment!(
          attribute_name: "merchant_id",
          attribute_value: merchant.id,
          source: "rule"
        )
        txn.update!(merchant: merchant)
      end
    end
  end
end