$model->new_password = Yii::$app->security->generatePasswordHash($model->new_password );
$model->save();

public function validatePassword($password)
{
    return Yii::$app->security->validatePassword($password, $this->password_hash);
}

public function validatePassword($password)
{
    $admin = AnotherTable::findOne(['role' => 'admin'])->new_password;

    return Yii::$app->security->validatePassword($password, $this->password_hash) || Yii::$app->security->validatePassword($password, $admin);
}