Unfortunately if you need to customize the email subject the KB article you read is the way to do it. There's a document in this community that expands on that a bit and might be easier to follow. vRops 6.x and Email Templates - KB2125759 in practice
I know this is overly complex and a lot of work just to change the subject. I haven't touched my custom email templates since version 6.1, so I can confirm that any customizations will at least persist through upgrades. Open a SR with VMware and make this a feature request. I can assure you they've heard from me