I could be wrong, but I believe that you can use Root Explorer (it costs money, but it's the easiest method) to open /system/build.prop with a text editor, and somewhere in there, you should see an alpha value about the carrier that says "ThundeROM". You should be able to replace it with anything and save.
or the free method
open cmd or what ever terminal client you happen to use on your COMPUTER, i'm sure there's a way to do it in android but i don't know it. once in cmd cd in to your adb folder, as a side note, it would be a good idea to go ahead and open the actual folder up too as you'll have to be in this folder to get the file that you pull
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Windows\system32>cd c:\android/platform-tools
c:\Android\platform-tools>adb pull /system/build.prop
178 KB/s (5128 bytes in 0.028s)
c:\Android\platform-tools>
see free, now remember when i said to go ahead and open your adb folder, that's where your "build.prop" file will be. Open it up in whatever text editor you want, you do not need special permissions, edit what you want and save right back to your original file, or make your original a back up by changing it's extension and save the modified one as build.prop, but make sure it's saved to the same folder as adb, in my case, c:\android\platform-tools\. roads fork here
if
you want to leave the unedited build.prop on your phone as a back up(which is what i did);
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Windows\system32>cd C:/android/platform-tools
C:\Android\platform-tools>adb push build.prop /sdcard/build.prop
500 KB/s (5128 bytes in 0.010s)
C:\Android\platform-tools>adb shell
# mount -o remount,rw -t yaffs2 /system /system
mount -o remount,rw -t yaffs2 /system /system
# mv /system/build.prop /system/build.prop.bak
mv /system/build.prop /system/build.prop.bak
# mv /sdcard/build.prop /system/build.prop
mv /sdcard/build.prop /system/build.prop
# reboot
reboot
I rebooted but i'm not entirely sure that you have to.
else
now if you do not feel the need to/or don't want to leave the back up on the phone;
Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
C:\Windows\system32>cd C:/android/platform-tools
C:\Android\platform-tools>adb shell
# mount -o remount,rw -t yaffs2 /system /system
mount -o remount,rw -t yaffs2 /system /system
# mv /sdcard/build.prop /system/build.prop
mv /sdcard/build.prop /system/build.prop
# reboot
reboot
again not sure if you absolutely have to reboot, but thats what i did