That got your attention 
In the movie Time Cop, the catch with time travel was that a person who went back in time could not be in the same place as their past self or the universe would implode or something.
Note: Movie nerds and Dr. Sheldon Cooper wannabes can save their efforts and keep the correction comments to themselves.
The same is true with a server or application. It really can’t exist twice in the same network or your career might implode or something. Think about it, you enable DR replication of virtual machines from one place to another. You want to test your DR, so you bring the replica VMs online … on the same network. Good things will happen, right, won’t they?!?!?! Two machines with identical names, identical application interactions on the network, identical IP addresses, both active on the same network at the same time during the work day … nope; nothing good can come of that.
Hyper-V Replica has you covered. You just need to remember to configure it after you enable VM replication and if testing failover is even a slight possibility (I”m sure you could automate this with POSH but I’m too lazy to look – it is after 9pm no a Sunday night when I’m right this post).
You’ll be auto asked after you enable Replica if you want to configure network settings. If you do (you can revisit later by editing the settings of the VM and expanding Network Adapter) then you’ll see this:
In Network Adapter – Test Failover you’ll have the option to set a Virtual Switch. See how it is not configured to connect to a network by default? Phew! When you do a test failover of a Replica VM, then the VM will power up on this virtual switch. Obviously this should be an isolated virtual switch (e.g. Internal or Private), and it should exist on all possible replica hosts (if the DR site is clustered), to avoid the Time Cop rule.