With the release of BC14 (BC 2019 Spring Release) we got a cool "new" feature when publishing our Extension to an OnPrem Business Central. So i started testing what was possible and compared it to our regular Synchronize function and the old Cside ForceSync. See below the results of my findings:
"Empty" = Not Possible.
X = Possible and you keep your data
O = Possible but you lose your data
As you can see we got exactly the same ForceSync which we had in Cside with the exception that we can now renumber a field without losing data.
I was a bit surprised with the Text to Code datatype conversion, I could have sworn that I've done this with a customer in Cside and that I kept the data...
Anyway I hope you can use this quick reference when in doubt :)