Currently if you generate a configuration through account.protonvpn.com/downloads the private key will only be valid for the server you chose. If you want to change the server, it's not enough to replace its public key and endpoint address for another Proton VPN server, you have to generate a new configuration with a new private key.

In an ideal world, I could generate a single configuration / private key, and later change out the VPN server endpoint. This would make it a lot less hurdle to switch VPN servers on routers.