Upgrade of Content Search Engine and related Content Engine data must occur as an in-place upgrade. As such, the data is migrated to version 5.0.0 and is no longer usable in the previous version of IBM® FileNet® P8.
To perform an upgrade in a migration scenario, create a duplicate of your FileNet P8 system by performing a backup and then a restore. Using the restored system, complete the migration from version 3.5.2 to 5.0.0. This will leave the original production environment untouched while testing is performed on the new system.
When you're ready to migrate the production environment to the current version, back up the system and then perform the in-place upgrade on the production environment.