This can be done easily but it's a little more involved than just admin list
For the admin list it's fine to just manually add entries to the file on the web server, but for this, since you'd (probably) be adding entries much more often, you'd want a script on the server to also take additions to the list.
Also, since it could take a second (or more) to get the ban from the server, you'd have to allow the player into the game, then kick then after you get the ban, or re-request the ban list every few minutes, and cache it
uh yeah you can
I'd be surprised if you can't
if it can be done for admin and clearing bricks it can be done for bans
The server gets their BL ID and does it with that.
This
You can ban by IP with add-ons, but that's it