Is there a way to have special firewall rules only for devices connected to the guest network?

I am running an openvpn server on my home network that allows me to connect to my house from other, outside networks. I have noticed that I can access the router configure page (192.168.1.254) while connected to the vpn. I would like to disable access to the router configure page. I thought of putting the openvpn server on the guest network to hide it from the other network devices. The openvpn server needs an open port to allow me to connect from outside my home network. Is there a way to specify open ports for devices connected to the guest network?

I have the Pace plc 5268AC router modem.

- Rose Peach