It is not a supported option to restore a 6.3 backup on a 6.2 system. Changes made to multiple tables/schema are most likely to cause failure during the restore.
However we can boot the CPPM on the other partition.
system boot-image [-l] [-a <version>]
NOTE: Say we are running 6.2.x version on one partition and 6.3.0 on other partition. The active partition is 6.3 and we take a backup on this partition.Now we want to roll back to 6.2.x version and we reboot CPPM with 6.2.x partition. We must not restore the backup (taken from 6.3.0 partition) after booting CPPM with 6.2.x partition even though they are taken from the same server.