I'm using Photon PUN, the only proprietary server used for the game is the authentication server. The game "server" is mainly used by the game just a relay for the clients to communicate with the host.
It's possible to make your own Photon PUN "server" / subscription (the free tier is 20 users at once), but I didn't expose a way to change out the server ID that the game tries to connect to. I'll consider adding a way to change that in some config in the next update, but at the same time, this spike in players isn't going to last forever. In about a week it'll be easier to get in.