The "hidden" email templates use variables, so you can't copy the HTML directly. If you replace those with their actual values though, it should work. I'd definitely recommend sending test emails to confirm though.
I managed to copy and customise a template to match the standard customised email templates, and I've saved that in a thread to be 'the norm' now. It's quite unique to have custom email templates because a fair few of the massive forums that are now using XF just don't bother. And all your emails appear to be the same. And it's becoming more of a problem because, let's face it, there isn't a better forum software. XF just does it, it just works. (As Jobs would say).
So yeah. Maybe get emails sorted out and you'd be leagues ahead of the rest.