I will answer only for TeknoMW3.
On Tekno, there is an auto-unbanner, which in the 188.8.131.52 (and 5) version make you stay on the server after a ban, until you get kicked by the admin.
You can find this unbanner in the barata's tekno multihack (You just have to remove the nullname ("...."), the solution is in the last pages)
Now, you can also use this ban bypasser, even banned, you will be able to come bck with this.
EDIT : For 4D1, you can be unbanned from servers with this.