If you have two Big-IP devices in a HA failover device group. One of them is active and the other one is on standby.
If you do some configuration work on the active device, can you view the configuration changes made before synchronising these changes to the stand-by device?
Active configuration change will not reflect to standby without Sync. And there is no such setting on Lb.
In device Group setting, you can see the which device has latest configuration based on time.
Please go through link, which will help you to understand Sync Group.
You're asking if you can do a config-compare between active and standby devices before doing a sync right?
There's no way to do this on-box, however if you have BIG-IQ you can generate a UCS backup from each device and run a compare.
Without BIG-IQ you could manually extract the bigip.conf file from each device and use a basic text-comparison tool.
this might help a little, it isn't very nicely shown but does this trick
show cm device-group <device-group> incremental-config-sync-cache