Tokens containing HTML in notification emails show HTML tags in emails

Problem/Motivation

I am using tokens inside emails such as the Registration Reminder email. These tokens come from custom fields I have added to the registration process on the Event Series entity, which can contain full HTML. Specifically, I have a field custom_registration_reminder that I place inside the Registration Reminder email as a token [eventseries:custom_registration_reminder]. This is so event organizers can place a unique registration reminder inside the reminder emails.

My Registration Reminder email set on /admin/structure/events/registrant/settings looks like this:

This is a reminder for your event.

[eventseries:custom_registration_reminder]

I am using Mime Mail module to send emails from my site in HTML format.

When Registration Reminder emails arrive, the HTML from the [eventseries:custom_registration_reminder] token is visible inside the email, not being translated into HTML. For example:

This is a reminder for your event.<p>Custom message should be here.</p>

I would like these emails to parse the HTML from the token.

Steps to reproduce

Add a custom "Text, (formatted, long)" field to the Event Series entity.

Have the content from that field print out in the Registration Reminder email set at /admin/structure/events/registrant/settings

Create an Event Series with content in the new field.

Trigger the Registration Reminder email to be sent and see that the HTML is not formatted properly.

Proposed resolution

I have success getting the formatting correct by changing code inside parseTokenizedString() in NotificationService.php and using Token::replacePlain() instead of Token::replace()

    return $this->token->replace($this->token->replace($string, $data), $data);

to:

    $tokenized_data = $this->token->replacePlain($string, $data);
    return $this->token->replacePlain($tokenized_data, $data);

I am not sure that this has no repercussions elsewhere. Or maybe my case is very unique. Any advice is appreciated.