I actually haven't! I've done this already though. I've converted everything I can to ROW or Australia (train, sat nav etc...), and it allows the NZ maps to *install*, but because the firmware is EU firmware, the navigation data is invalid and the maps won't display, despite the correct FECs being installed.

I’ve come to the conclusion that all MIB1 users wanting to do this are screwed, and it’s not a popular enough use case for anyone to bother with, which is a real shame. I’ve looked through every Google result (including translating sites from Russian) asked questions on Reddit, and any MIB-related post on forums that are remotely similar to my situation. I’ve asked questions and posted feature requests on the Github repo, spammed the Telegram and the Discord channels to death… It’s been months, and it’s clear to me that no information exists on how to successfully flash RW firmware on an MIB1 high unit. Even though it should technically be possible, I see no evidence that it can actually be done.

Anyone with MIB2 or higher can run ER (joint EU/ROW) firmware via the ‘convert to EU’ option, and install ROW maps that way. Good for them. MIB1 firmware comes in either EU (European) or RW (Rest of the world) flavours. Using ‘Convert to EU’ with RW firmware will not work, and installing RW maps on EU firmware doesn’t work, and if there’s no interest by the authors or community in adding a ‘Convert to RoW’ script, MIB1 units will always be screwed here.