8 – How can I use one of the pre-set email texts for user registration in a custom module

At /admin/config/people/accounts, there are several stock email messages set.

How can I use one of these when I am sending emails from a custom module?

The text that’s being used in “Welcome (new user created by administrator)” is all that I need, plus there’s the bonus that our client can edit this email in the future if they want to.

I can send the message easily enough using:

$params = (
   'title' => "My Title",
   'subject' => "An Account Has Been Created for you",
   'message' => Html::escape("Some text here")

$result = $mailManager->mail($module, $key, $to, $language_code, $params, NULL, true);

Is there a variable somewhere to get the pre-entered text?