Well, I motored down to Christchurch last week and had two business days there to get some things done. An online search led me first to https://soundworks.net.nz/. Greg was very helpful, although his guy was away for the week, he knew someone else and would check for me. In the meantime a further search turned up this promising result: https://protechsolutions.co.nz/products/bmw-ccc-radio-conversion-from-japan-to-new-zealand?_pos=2&_sid=64a66e6ba&_ss=r
Exactly what I want, so I booked them first thing next morning. On arrival they stated 'No play, no pay!', so I said go ahead! After half an hour Greg phoned back & said he'd found someone who could do it that day - I said thanks, but it's being done right now... Well, turns out that while they could extend the FM band from JP to NZ, they couldn't get any reception - apparently some of the code had already been messed with, so the usual fix didn't work. While they were undoing their attempt, I called Greg back & said 'Help!' He said come & see him after lunch.
In the meantime I headed to Vantage Auto Diagnostics (https://www.vantageauto.co.nz/) for another issue (see https://bimmersport.co.nz/topic/69604-e91-key-fob-required/), and quickly figured out this was where Greg was going to send me after lunch. When I saw Greg later, sure enough he said go straight to Vantage - since I'd been mucked about already, he didn't want to clip the ticket as well.
So back to Vantage, where young Christopher seems to know the BMW computers inside out, and he got stuck in straight away - with a quote only 2/3 of the first attempt! 40 odd minutes later he was done, only one issue - everything worked as desired, station names and reception perfect, except the manual tuning mode didn't show the full NZ frequency range. Apparently some of the code had already been messed with, so the usual fix didn't work fully!
I departed happily for the city, wandered around & had a coffee. Went back to the car about 3:30, started the car, and - no AM or FM functionality at all. Bugger. Long weekend about to start...
I drove straight back to Vantage & luckily Christopher was still there. I explained the issue and he wasn't too happy, but he hooked up his diagnostics & went to work. Half an hour later he said it was all done, even better than before. Because apparently some of the code had already been messed with, he'd bitten the bullet & done a full reflash of the 5 CCC modules. Now it all worked perfectly, even giving me SW and LW alongside MW. I was so pleased with his work I paid him the extra 1/3, and headed for the hills with local stations blasting!
Honestly I can't recommend these companies highly enough for there willingness to help out at short notice. Top guys!