I have to repeatedly ban the same peer because it eventually (too soon) gets unbanned and then my daemon output spams me with "peer claims higher version that we think." This issue persists with this one peer, so I'd like to ban them permanently.
There is no command to permanently ban, but you can set a lengthy ban time using the daemon command
ban <IP> [<seconds>], or using the RPC method set_bans.
So if you set the seconds parameter to 4294967295, that will ban for just over 136 years.