After re-imaging and expanding the switch nand at least 10 times during the dance to get the switch to see the larger 128GB nand I eventually got it working, but didnt make a note of exactly how I got it to work, damnit! I had to do it again to make some better instructions, and if I had to do it again, I may as well go large, as large as I can find, 256GB!
I saw guides online for upgrading the switch NAND, first on gbatemp and reddit, which linked to John Pascoe here: http://pascoe.pw/2018/09/switchnand.html and he quotes http://bbs.duowan.com/forum.php?mod=viewthread&tid=46505080&from=singlemessage After reading through I convinced myself to give it a try. I first bought a few blank USB pendrives and EMMC chips from taobao, pre-balled, so that I could try to teach myself how to solder BGA chips with hot air, this also needed a hot air re-work station, so i bought one of those too from Taobao, 50 dollars lighter and with a small stack of dead USB boards I realised that I wouldn’t have the nerve to do an expensive EMMC board, so whilst carrying on my expirements on cheap boards, I sent a 128gb chip, the Samsung KLMDG8JENB-B041 linked below, along with a replacement Switch EMMC board, to a professional to be reworked. https://item.taobao.com/item.htm?id=537061791727&_u=u20k5lp07285
The blog has landed!