I was just wondering if I want to change the IP address of an instance running in my Proxmox, do I also have to change the IP that is inside Proxmox? Will it cause problems?
Assuming you mean changing the IP address of a VM or LXC container that lives on your Proxmox server, that is fine to do.
IP addresses "inside Proxmox" would typically only be visual purposes like in the Summary or if you have hard-coded those addresses somewhere manually.
