Hi Stuart Green,
My name is Eran and I'm the manager in Check Point R&D responsible for the core infrastructure of the Management server. Indeed in R80.x we're not yet supporting migration of a Security Management server into a Domain on a Multi Domain server. My team and I are working to complete this gap these days, and we target to reach EA few months from now. We would be happy to provide you an EA build on top of R80.20 as soon as we're ready so you could install and test it. You're also very welcome to provide your feedback and influence on the usability. Our plan is to integrate the code to an official version later this year.
This is a call for any customer who's waiting for the ability to migrate a Security Management server into a Domain on a Multi Domain server over R80.20 and above! You're welcome to reply to my comment and register, R&D will approach you in the next few of months to provide an EA build on top of R80.20.
migrate_SMS_to_MDS