Here someone posted this in another thread to do it without winterboard and takes less than a total of 5 mins to do:
1. Download iFile in Cydia. It's shareware so you could use it for free.
2. In the iFile app go to /var/stash/Applications/MobileSMS.app
3. Look for Icon-Small.png, Icon-Small@2x.png, icon.png and icon@2x.png, click edit and then the little arrow in the lower right, then --> copy
(you might not need all 4 but this is what I did and it works perfect.)
4. Go to var/stash/Applications/biteSMS.app and select edit and then paste --> overwrite.
5. Reboot/Respring
6. biteSMS icon should now look like the default SMS picture.
* Copy the icons from your MobileSMS.app app into BiteSMS.app