In any execution of the migration utility, before the utility migrates your customizations from the backup directory to your new installation, it creates a backup of certain files in your current new local and stores it in a .rollback_<version_timestamp> directory. Also, it records the version and timestamp before any migration.
The rollback option allows you to reverse the changes made by the migration utility by restoring the local version in your new installations using files from the .rollback_<version_timestamp> directory. Rollback will contain only those locals which are part of migration.
In some scenarios, if a file is copied to the new installation with .<old_version> extension, then this file is not deleted when a rollback is performed.
You can use the rollback option only after an in-place upgrade or if you have previously run the migration utility either in the SAME_HOST, DIFFERENT_HOST or UPGRADE_NEW modes.
Perform a rollback describes the procedure for carrying out a rollback.