tokens – How can I combine a confirmation mail, especially text for [simplenews-subscriber:combined-url] in simplenews?

I would like to custom link for the (simplenews-subscriber:combined-url) which appears as http://example.org/newsletter/combined/123/123456789.....

It would be better if the link appears as Subscribe in the email, but I don’t know how.

Preprocess function seems to be OK in the simplenews.module file.

$variables('subscribe_text') = t('Subscribe from this newsletter', (), ('langcode' => $variables('language')));

I don’t know where I can edit (and I’m not sure it is the right solution).

{{ subscribe_text }} : (simplenews-subscriber:combined-url)

In MailBuilder.ph file, buildCombinedMail(array &$message, array $params) could help me, but I’m not sure it is the best way.

$body_key = $actual_changes ? 'combined_body' : 'combined_body_unchanged';
$body = $this->config->get('subscription.confirm_' . $body_key);
// The changes list is not an actual token.
$body = str_replace('(changes-list)', $changes_list, $body);
$message('body')() = simplenews_token_replace_body($body, $context);
$message('body')() = 'my custom message here';

Maybe, the best way would be with a template, but I don’t see one for combined confirmation emails, and I don’t know how to add a custom template to Simplenews module. (There is only one template for newsletter, simplenews-newsletter-body.html.twig.)

Do you have any idea?