For testing multiple Vault instances on a local device, one method for implementing unique addresses for each Vault instance is to add an alias to the loopback network interface. Please be aware, this method is recommended to use only for testing purpose not production use.
A loopback alias with an address of 127.0.0.2 can be created in MacOS with the following:
sudo ifconfig lo0 alias 127.0.0.2
And to delete alias
sudo ifconfig lo0 -alias 127.0.0.2
This is not persistent – the alias will not survive a reboot. If you need to keep it permanent, a new launch daemon file needs to be created. For more information about launch daemons and how to configure them, refer to Apple's documentation.