I have the following:
1 ePO (ePO1) server in a subnet with all servers and workstations managed.
1 ePO (ePO2) server in a different subnet, different name without servers and workstations managed.
The security keys from ePO1 already copied in ePO2.
If ePO1 goes down, What is the way to manage workstation and server with ePO2 if I can't transfer system to ePO2?
change values in sitelist?
For ePO2 to manage those servers/workstations that were reporting to ePO1 an ePO2 agent will need to be installed on those servers/workstations (granted that ePO2 is able to communicate across both subnets). Even though the keys have been shared through the registering one server to another server does not mean that you would be able to manage those systems WITHOUT first transferring them or installing an ePO2 agent. Essentially, the shared keys/registering process only allows for the transfer of systems, tasks, policies ... not the management of those systems.
If the scenario is; ePO1 goes down and you would like ePO2 to manage those systems - sounds like a cold / hot spare: page 220 https://kc.mcafee.com/resources/sites/MCAFEE/content/live/PRODUCT_DOCUMENTATION/25000/PD25519/en_US/...