Thanks for the info all. I hadn't realised that there was a delay to the read stats so that's useful to note. Appreciate that 10-speed, rim brake, wheels are something of a niche in today's market!
I don't know enough about the various freehub swaps (exploded diagram of the hub is here: https://si.shimano.com/pdfs/ev/EV-WH-7900-C50-CL-R-3136.pdf). Seems like machining it would work, but that is something of an agricultural option. The option based around 11:10 speed cassettes seem exorbitant! Will give it a few more days and see if there are any takers.
If anyone has a lot of time on their hands, then there is a long thread on WeightWeenies https://weightweenies.starbike.com/forum/viewtopic.php?t=115919