But, yes, procedure is standard. Go to TWRP, put backup in right folder (named by s/n of your phone), Restore.
2. can we return back to a JBBL using a previous personal TWRP restore, or do we need to flash the original JB ROM? (to return to JBBL)
No one can switch between JB and KK w/o flashing related bootloader!
I can make complete Telstra ROM 4.4.2 (as that stock 4.1.2 one ) for easy install, but it will be unlocked bootloaders only, cause images will lack signature. Locked should go through OTA. Or we all can wait for official 4.4.2 RSD/SBF release from Telstra.