Q: I enabled Hyper-V Replica for a virtual machine and made a change on the primary; however, that change isn't replicating to the replica--why?
A. This is by design. When a virtual machine (VM) is replicated initially, the configuration of the VM is replicated to the replica target; however, after the replica is established, the VMs are now effectively separate with only changes to the storage of the source replicated to the target.
Any configuration changes to the source VM--such as adding memory, virtual CPUs, network adapters--would need to be manually configured on the replica VM.
This is actually useful for several situations. For example, a failover IP configuration can be configured for each network adapter, which is used in the event the replica is activated. You would want the failover IP configuration on the replica side to be configured for the replica site IP scheme, while on the primary site you would want the failover IP to be its primary site address (its normal address).
The reason you would configure the primary with failover IP would be this: Imagine a scenario in which you perform a failover to the disaster recovery location, then once the primary site is available again, you want to fail the VM back to the primary. If you didn't have the failover IP configured for the primary VM, then it wouldn't have the correct IP address for the primary location and would keep the disaster recovery location IP.
