if you are already jailbroken, you can re-run redsn0w to get the untether or you can search for "corona" on cydia. There is no need to update in iTunes and re-jailbreak.
baller1308- a backup of your phone does NOT store jailbreak data, tweaks, themes, settings, etc. You have to have specific "cydia backup" apps for that or you will have to manually download all of your cydia stuff again.