I know its late but for any new comers like myself the solution is to migrate or copy paste uasset files from projects using older version or same version of unreal engine to the project of your choice upgrading in this way is ok after that all you have to do is (if you didnt migrate assets) close the project and reopen it (might need to delete intermediate, binay, saved and DerivedDataCache folders if you do this you need to right click on the uproject file and generate visual studio project files) as for downgrading from newer version of unreal to older your best shot and maybe only option is to copy from blueprint editor to notepad and to the new projects blueprint editor