The eri.xml file inside "/system/framework/framework-res.apk" contains the carrier name. This is a binary file, so it must be decompiled to get access to the XML files within it in ASCII form.
I've seen some Android websites document editing this file then rebuilding the apk and pushing it back in place of the original. I tried this and screwed up my system (thankfully I had a system backup to restore from). The simpler approach is to leave that apk file alone and simply copy the edited ASCII eri.xml to /data. The OS should pick it up (at least this is the case on Cyanogenmod based ROM's). Worked for me.