The last time (2017) I finished a ex CAI (QR issue) DONEx and restarted with a LONEx(also QR issue) flying the first 3 segments. Early in 2018 I converted this to a DONEx paying only the difference in the fares as of the time of the purchase/issue of the LONEx.
Both were handled by a travel agent in Perth.
Sometimes a competent TA is useful when wandering
Fred