Will the configuration of LB-8000 take effect if I do the setup in backup LB-8000?

Yes.
LB-8000 has bi-directional sync function to ensure the setup done in either primary or backup takes effect.
After you make a configuration on one LB-8000, the configuration on the other one can be synchronized, either automatically or manually.
The sync will be automatically done if you set up through web GUI, but in CLI you have to manually sync two LB-8000.
The system time in two LB-8000 is always synchronized so that the valid setup can be decided by time stamps.