Sorry for the late response.  I'm not sure if this question is still valid but below is a link to the AccessControl code I gave to the DoS clan a couple years ago.  It contains the permanent mute control you want.

http://emac.dfbgaming.com/dFb_AccessControl_DoS.zip

There's two files- one file that you load into the server's AccessControl class and another one that extends the web admin.  It's actually not a mutator and you need to modify the command line differently.  I'm not sure how much control you have to change the command line.  One of the reasons why this wasn't a mutator was to keep the server pure.

After you copy the files to your server, you have to add [i:60f4a2b1fb]?AccessControl=dFb_AccessControl_DoS.dFb_AccessControl[/i:60f4a2b1fb] to the command line.  Then open up UTWebAdmin.ini and add [i:60f4a2b1fb]QueryHandlers=dFb_WebControl_DoS.dFb_WebAdmin[/i:60f4a2b1fb] under the [WebAdmin.WebAdmin] section.

In the web admin there should be a new link on the sidebar to add people to mute.  It should work the same way you ban people.  Unfortunately, I don't think I added any admin console command to add people to the permanent mute list?