Recently we also observed same issue, around six months back we migrated one propertt from DTM to launch but due to some issues we did not configure same in production,now the problem is we did some changes at DTM side and again need to migrate to launch, by seeing this scenario it will not create any issue for you
You can upgrade to launch once again with out deleting the old property, when you upgrade to launch it will create new property in launch with the timestamp
Once everything is working then you can delete old property in launch