Is there a way in F5 LTM to verify changes before sync

There really isn't a way to verify changes prior to sync. Probably the best way to handle this is to have a change control policy, make regular backups, and always sync from the active unit to the standby.

You can look at the Network Maps on the active and standby, but if you have a large configuration you may not see differences. Also be aware that this will not catch changes to APM or ASM modules or changes to policies.

If you sync and determine that the changes were undesirable, you can always restore the back up just made and sync in the other direction.