Yes, it is possible to add multiple IP addresses to your domain.
To add a new IP address to your domain, open your domain group and locate your domain. Click on the "Actions" button and scroll down to the "Additional IP Addresses" section. There, you can add and remove IP addresses from your domain.
Please note that your IP address needs to have at least 1 free slot to be added to the domain.
Using additional IP addresses is a great way to load balance your DNS or set up private nameservers when your registrar requires unique IP addresses.