An App named "Customize" will do this for you. Goto: http://thespicychicken.com/ and click on the word "customize" to get info about the program. You can install Customize using your "Installer" program if you have installed that.
But, if you want to do this with iBrickr, when you start up iBrickr click on "applications" then scroll down until you find "Customize". Version 1.03 is the latest as of right now.
Also, you'll need to install "Designer Image Set" v.0.2. You can find that also when you start up iBricker and go to applications, OR if you're using Installer, it is under "Images" in the Installer.
Once installed, it's merely a matter of clicking on your new Customize icon, then clicking "carrier image".