This is not my experience.

Earlier this year I bought a AONE4 ex-JNB issued by QF for departure in December. I got it at the old price before the massive price hike. A month ago I went to QF in London to have it re-routed. Despite the fare having more than doubled ,the only charge I paid was £25 for the reissue. This is not a OW charge but a charge levied by QF for "Professional Services". If my memory serves me correctly you can have unlimited changes up to the date of departure.