is it possible to change interface name in the firewall

[BusinessUser]

after they have been named,

instead of deleting them and the firewall rules?

[pminarik]

Renaming is not possible. You would need to either delete and recreate, or manually edit a configuration backup, then restore this modified configuration (reboot required).

As an alternative, you can consider adding an alias to an interface to make interface identification easier. The alias will show in the GUI only, however.

[mle2802]

Hi @BusinessUser,
I don't think this possible. However, you can use an alias for the interface. 

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Rename-interface/ta-p/221982

Regards,
Minh