You need a downtime anyhow. I would remove both devices out of the network and just add the new ones.
After that you have to reconfigure the VLAN-to-port-mapping and reenable the AutoVPN. The rest of the config is fetched from the dashboard.
If you found this post helpful, please give it Kudos. If my answer solves your problem, please click Accept as Solution so others can benefit from it.