You can clone the current network and add this new device to that network, but you should not enable auto VPN to avoid problems.
But honestly the swap is so simple that I don't even know if it's worth it. At the very least, I would keep the firewall updated to the same version as the current one.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.