When converting an island from 1.0 to UEFN, there needs to be a warning message that the creative island will no longer show in Creative and that process cannot be undone, so the user knows (some functionalities of 1.0 break upon conversion, like the SAC button, accolades and persistence) and until those are added to UEFN, it is destructive to perform this process because then you are stuck in UEFN and cannot go back to what you had. Also prompting them to duplicate the island first and use the duplicate to convert, will help users from not losing content (that can be a button on the warning popup too, “Duplicate then convert”, “Convert existing”, or “Cancel”. If user presses “Convert Existing”, UEFN should give a second popup warning them of what is mentioned above ^. If the user confirms, then the process continues.
Also it would be nice to show a list of things that currently don’t work with UEFN (but do with 1.0) when trying to convert, so the user knows if their content will break or not.