If your Zigbee or Z-Wave device is currently backed by a Custom DTH (not published in the ST repo) and you have a replacement community Edge Driver on your hub, ST will migrate those devices for you to the installed community driver (What is highlighted in Option 4 from the FAQs).
Please note this will not work for Lan devices.
Also, because we don’t know the entirety of the custom DTH was and what it’s replacement driver is, we cannot guarantee the expirence will be exactly the same (as we haven’t reviewed the code of either and it isn’t in our repo).
When in this situation, I recommend to please check the name of your preferences between the Customer DTH and the Non SmartThings owned Driver. If they are not the same, preferences will not migrate.
I don’t know the previous communication you received, if it’s helpful to you I’d be happy to review it if u send a link.