Hi,
It turned out special characters aren't a problem. I was just about to reset the config when I decided to try the old "turn it off and on again" solution and it worked!
It booted up and I'm able to login again.
Yay!
/ip firewall filter add action=accept chain=input dst-port=8291 disabled=no in-interface=ether1-gateway
ip route add dst-address=0.0.0.0/0 gateway=192.168.1.1