Uh, not sure what key you're talking about. Mode is not a key on the keyboard, it's the name of a script. You can search on google for "pushmode mirc" without the quotes, and it finds a script of that name on hawkee, and there's no button pushing involved. It's a script that reduces your chance of flooding by combining bans like "mode +bb #channel nick1mask nick2mask"
Something else you need to be aware of is that your ban list is not an infinite free lunch, and there will come a point where the ban fails because the list is full. If you type
/version
most networks will repeat the message they show during CONNECT which shows their settings.
there should be something like MAXLIST=beI:100 which means the banlist exceptionlist invitelist are all limited to 100. If that's not there, it probably has some other unknown limit, and you might need to make a dummy channel to see how many you can stuff into it before it stops actually adding them.
Once the banlist is full, you'll either need to delete older ones, or find a way to combine some
Unfortunately you can't trust the dates listed, because each time you recover from a netsplit, it changes the banning nick to the server name and changes the timestamp
