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As I know, to change domain name, you can still set up DDNS by configuring your router.
Enable DDNS on the WAN interface of your router (you can find free ddns to use them) and configure the necessary port forwarding rules to forward traffic from the WAN to the LAN IP address of your NAS. Once this is done, you can access your NAS using your domain name and the specific port number you configured for the port forwarding rule.

You can change the server name on the NAS, the NAS326 model uses the server name as the login page url in the local network, go to Control Panel > System > Severe name. You can change the server name there.