That all depends - is this a HW change only or also an update? Usually, if no IP or name is changed and no VPN used, you proceed like this:
- take a migrate export from SMS (see sk108902: Best Practices - Backup on Gaia OS, use -l for log export)
- if needed, save GAiA config (routes a.o.) using sk102234 - Backing up Gaia system level configuration
- configure new GWs
- configure and migrate import new SMS
- do the changes/additions needed for new ports/nets
- edit GW config and establish SIC with the new GWs
- install policy
CCSP - CCSE / CCTE / CTPS / CCME / CCSM Elite / SMB Specialist