Unable to override account creation email template

Question

I need to modify the welcome email sent to user upon new account creation. I need to do this in my custom module. I tried to override the function sendNewAccountEmail in Magento\Customer\Model\Customer using preference method and also using plugin method. Both were not working.

For preference method I added the following

In Vendor/Module/etc/di.xml

<preference for="Magento\Customer\Model\Customer" type = "Vendor\Module\Model\Customer" />

Added Customer.php file in the location Vendor\Module\Model\Customer and added the following code

    public function sendNewAccountEmail($type = 'registered', $backUrl = '', $storeId = '0')
{
    echo "It's Working";exit;
    $types = $this->getTemplateTypes();

    if (!isset($types[$type])) {
        throw new \Magento\Framework\Exception\LocalizedException(
            __('Please correct the transactional account email type.')
        );
    }

    if (!$storeId) {
        $storeId = $this->_getWebsiteStoreId($this->getSendemailStoreId());
    }

    $this->_sendEmailTemplate(
        $types[$type],
        'customname/email/account_email_template',
        ['customer' => $this, 'back_url' => $backUrl, 'store' => $this->getStore()],
        $storeId
    );

    return $this;
}

Still it's not taking the Customer.php file in the module.

echo "It's Working"; is not displaying.

What is the correct method to follow? I tried the plugin method also. It's also not working.