Buh-bye "break" command and thank you but no thank you cck (no offense I'm sure you've got some great uses, but you also confuse the heck out of me and I see no documentation that anyone this side of a systems engineer can figure out).
After much futtzing, I've figured out how to implement teasers as a seperate textarea from the "body" field using on the exceprt module and contemplate (barely).
A few caveats first:
* This is tested for 4.7.3.
* It is more convenient to set up with a new site, but it is doable on an old one (*see comments at the bottom for more)
* There are no code hacks to anything, but because of the way this solution uses existing functions you should expect to accomodate some special needs when it comes to updating your installation since this uses the existing "teaser" and "body" columns (within the node revisions table) in a different way than a stock installation does when teasers are autogenerated or created with the break command.
* Teaser length settings in admin/settings/node will have no effect on any content type which is set to have a manual excerpt. What you enter in the teaser text area is what gets output. Am planning to add a character limit on the teaser at some point. If someone beats me to it - that would be awesome.
* It is possible to undo these changes, but you would need to take care of any teasers (e.g., get them transfered from the "teaser" table cell to the "body" table cell in the node revision table) which you generated while this setup was active.
So (finally) here it goes (if you are trying this on a site with pre-existing content read the addendum first):
1. Get the 4.7 version of the excerpt module. There are some patches people have put up in the issues threads. Don't use these - they seem to break the "read more" functionality. The module works great as is. Or you can download this one which I've modified slightly for my needs.
2. Get the 4.7 version of the ConTemplate module (another fabulous creation by JJeff)
3. Install both modules
4. Turn on excerpt functionailty (e.g. seperate textarea for teaser) by going to /admin/settings/content-types and selecting each content type and turning on/off "Manual excerpt" for each one.
5. Once you're done with that go to /admin/node/template to set up contemplate. You'll be greeted by a screen which lists all of your content types and has a link which says "create template" next to it. Click this link for each content type you want to enable a seperate teaser for, scroll down to where it says "Body Template", paste in the following:
print $teaser; print $body;